 In the last lecture, we looked at the importance of precursor method. As I emphasized in the last lecture, precursors are a very convenient route and wet chemical route to prepare complex metal oxides. So, you start in solution, but you end up with a crystalline solid where the atoms and the anions take their position in the right symmetry. So, this involves both kinematic approach as well as thermodynamic approach. In precursor method, I distinguish between solid solution precursors and simple precursors. Today, before I discuss more with the simple precursors, I just want to touch one more example to refresh our idea about solid solution precursor. Just to recap what is the importance of it and then we will look more into the simple precursor routes. And this is the precursor wheel as I put it in simple form. A lot of precursors can be used to bring about the metal oxide formation, but one route is solid solution precursor route, another route is simple precursor route. So, just one more example on solid solution precursors, we can think about zinc magnesium oxygen system using the same concept of isostructural cunnoline complexes. In the last lecture, I emphasized about the importance of structural similarity and once you pack all the corresponding atoms into that crystal, then when you decompose it, the corresponding metal oxide that you get will also have the finer and atomic level doping can be achieved using such a principle. Now, this cartoon shows how the x-ray similar patterns can be exploited for making solid solutions. As you see here, this is zinc Q2 and zinc Q2 is nearly cubic in its x-ray pattern because you have only three obvious or major peaks and they are nearly equidistant. So, just by looking at the precursor x-ray, one can guess what sort of crystal symmetry it can have and in this case, because of equidistant peaks, you can easily map it to be a cubic because of higher symmetry, you get very less peaks whereas, when it is more complex, you get more peaks. .. So, if you look at magnesium Q2, if you take magnesium Q2, again there is a similarity between Zn Q2 and magnesium Q2 and therefore, this gives us a privilege to dope magnesium and zinc together. So, the next three solid solutions are with varying percentage of magnesium from 5 to 15 percent. So, you can keep varying it and as you see here, all these precursors are having this low degree reflections or low reflections at around 7 degrees. So, once you ensure that such a solid solution precursor is made, then you can try to look at the possibility of converting this into the corresponding oxide. The values, the major peaks are all listed here. As you can see, they are all closely matching. Therefore, we can say that they resemble the same crystal symmetry and if you take the precursor itself, they are highly photo luminescence, especially zinc Q2. Therefore, when you put magnesium Q2, you can try to see whether there is any systematicity with the doping concentration of magnesium and as you would see here very clearly, this is the expanded version of this region. Just to highlight that as you dope magnesium in zinc Q2, you can see the peak maxima is shifting towards the blue region which you would expect because magnesium has a different size and it is also showing emission near to blueish green. So, you can take clue from PL that magnesium is indeed getting dope. That is why you see the peak shift and if you look at the thermogravimetry, it gives you idea about how you can translate this quinoline true oxide by taking magnesium Q2 and zinc Q2. If you look at the thermogravimetry, zinc Q2 is decomposing somewhere around 450 degree C, whereas magnesium Q2 is decomposing around 550 degree C. So, you need to have some idea about how the precursors decompose on their own. By just having an idea of zinc Q2, suppose you are decomposing the precursors at 500, what it means is you are you are going to have a incomplete decomposition. Therefore, analysis of thermogravimetric traces is very important and as you would see here the DAC plot is clearly showing the dehydration step and the decomposition step and melting before the composition all are prominent and this gives an idea how we can translate it into the oxide and this particular x-ray diffractogram shows how zinc oxide with magnesium oxide can be ably substituted and as you would see here up to 15 percent there are no traces of any peak of magnesium that is coming here which means absolutely magnesium is going into the zinc lattice zinc oxide lattice. Therefore, you can say that magnesium is getting substituted and it is not a phase separation. So, this is a very useful way that you can try to dope magnesium into zinc oxide and the absorbance spectra also clearly shows that there is a blue shifted absorbance and as you would see zinc oxide is absorbing which is denoted by this curve and there is a shift towards the blue with the periodic doping of magnesium and since magnesium oxide is a high band gap material magnesium oxide itself would come somewhere around here and therefore, progressively you can see the bandage is shifting towards the blue region, but what we have to understand the PL emission does not seem to really give the necessary feature that we look for for example, zinc oxide is showing this band emission which is very useful and which is very conclusive of zinc oxide particles they show a very small gap small peak and then a very broad peak around 500 this is due to defect chemistry and as a result we can see irrespective of magnesium oxide doping that defect induced emission is much more compared to band to band emission. So, we may be able to prepare at low temperature we may be able to prepare the same thing using a novel method, but what is important to understand is how we can get this surface free defects and that is very critical. So, just a mere consolation of a low temperature synthesis or a solid solution approach does not guarantee the end product what you desire it may be compositionally good, but then there are defects which are intricate with the precursor model. So, this we need to bear in mind and when we come to simple precursors we are now going to talk about several combinations. We can talk about nitrates, hydroxides, acetates or even chlorides all substituent metals for example, if I take metal 1 and metal 2 corresponding nitrates I expect those two blend together. So, that I can get the resulting oxide by decomposing it, but there are some nitrates which have a very clear crystal symmetry therefore, one can go for such match also and these are more or less hygroscopic that is why I grouped these together hygroscopic and because nitrates hydroxides and acetates sometimes are hygroscopic even chlorides we can add here and because of that the use of a nitrate precursor or chloride precursors are very much restricted because if you are going to bring two metal salts then hygroscopic ones will react as a result you would not get a perfect control over the stoichiometry. Whereas, carbonates and oxalates are mostly they are air stable and as a result it is better for us to use oxalates or carbonates as precursors because even when you try to weigh those starting materials you can precisely weigh that therefore, the error involved in your stoichiometry will be very less and thirdly the most used among precursors is solgile precursors. I will come to this shortly from now solgile precursors are mostly alkoxides when you treat any metal with alcohol then you can get metal alkoxide and therefore, that is largely used but as the name itself suggests there is a phase which where you get a salt phase and then you progressively take it to a gel phase and then it brings about a metal oxygen framework which will serve as a good precursor for getting metal oxide. So, I am going to take you through all these three examples with several approaches. So, in the next few slides I will give a representative idea of how this simple precursors can be used. Next one as an example I want to quote how zinc oxide can be made zinc oxide is not only used in classical electrical conductivity or sensor applications of UV radiation it is also used in variety of other application. Therefore, there are for some applications you need a very stringent control on the stoichiometry or purity there are certain applications where you really do not need such phase purity. For example, if you are looking at fastening the color for any equipments sports application zinc oxide is used because in all these polymers you need to put the zinc oxide to filter or to absorb the UV radiation. So, that the coatings or the coloring agents that are added are not degraded. So, to fasten the color zinc oxide is used pigment in cosmetics it is used as a base because you can make very fine zinc oxide and it is non toxic and in ceramics you can use it it is also used to bring a good blend between brass and rubber. Therefore, zinc oxide comes as a very good one, but zinc oxide is not just used as a additive, but zinc oxide also has a very peculiar application as a surge arrester for high voltage applications zinc oxide is a very potential one. Now, zinc oxide is a white powder and you know there are many ways we can prepare that I will just show you how simple precursors can be used and how it can transform distinctly. This particular cartoon tells us that zinc oxide thin films can be made by merely spin coating or spray coating zinc nitrate solution zinc acetate and zinc chloride solutions. So, you can just spray it and then decompose that into a film and as you would see here in this left cartoon this is the region where you need to get all the reflections in the right intensity and as you would see here the chloride precursors are very poorly represented and then the acetate precursors, but what you see here as a good crystalline phase is coming from nitrate. So, among nitrate chloride and acetate it gives us a very clear clue that nitrates can be considered as a very useful one because it gives a crystalline phase and corresponding thin film also you can see the morphology completely changes in case of chloride because the chlorates do escape during the heating process they give discontinuous grain growth. Therefore, you do not see any grain growth which is continuous and although the morphology looks attractive, but electrical continuity is missing between the grains and therefore this particular film might lack percolation and in the case of chloride based ones you see lot of segregations or larger particles which are crystallizing. So, this is not a smooth growth comparatively nitrate appears to be much better, but then there are also lot of voids and the films are not very smooth. So, precursors can be used, but then we should have in mind the limitation that comes along with every precursor, but all these precursors can be decomposed in less than 300 degrees centigrade. And if you look at these films there are transmittance technically the transmittance has to be somewhere around 90 percent. So, you would expect a fall like this for your absorbent spectra or in most cases using PLD or MBE method you can get a transmittance up to 80 percent, but using this precursors you can see that the transmittance is going down very abruptly and therefore the quality of this films are not very resolved as in the case of PLD. However, when you look at the band gap band gap clearly shows that it corresponds to 3.3. So, for electrical resistivity purpose all the films seem to match with the desired values whereas the for photonic application or for other applications which are critical with the microstructure we seem to see a very inferior film. .. Let us take another example of garnets. Garnets are those which have A3 B5 O12 sort of stoichiometry and these are all garnet crystals naturally occurring. For example, this is nothing but YIG crystals which occur in nature and to make such crystals or powders it is very very difficult because it involves very stringent thermodynamic requirements. So, how do we achieve that? For example, case of YIG which is iron garnet this has very wide range of applications including microwave, optical, magnet optical applications and also in non-linear optic applications it has been used. Now, how do we do that? One example is using a citrate nitrate gel because when you try to deposit such layered structure with complex stoichiometry it is always important to go for a slower method rather than a rapid method because you can get a much more stoichiometrically stringent or controlled stoichiometry in the final oxide. So, citrate nitrate gel is one of the best methods why we can use citrate nitrate gel is they almost behave like a combustion mixture because citrate forms the fuel part nitrate forms the oxidizer part but the best part here is instead of keeping it in solution you can isolate that as a solid as a result it is possible to isolate a solid which can act as a precursor to give the corresponding oxide and this is the difference between the regular combustion process which I discussed in one of the earlier lectures and the combustion that comes out of a citrate nitrate gel. So, if we do a thermal decomposition you would see exothermic peak coming and that is mainly because of the reaction between the fuel and the oxidizer in the gel. Now, as an example quoted by this person we can actually use a yttrium aluminum garnet or we can also make yttrium iron garnet. So, we can make this precursor using citrate nitrate gel and then as you would see in the room temperature mostly they will remain amorphous because they actually undergo a sol-gel reaction where a disordered metal oxygen bonds are made. So, in your order to crystallize this you have to heat and this is a usual protocol in the sol-gel chemistry. Therefore, if you keep heating it you can get very good phase or a single phase compound, but sufficiently at lower temperatures. So, this is one approach by which one can make complex oxides. I will come to the chemistry of this sol-gel in the later slides in this lecture. Dentate is very useful mainly because if you look at the structure of citric acid you have a carboxylic group here, you have a carboxylic group here and then there is another carboxylic group also here. When metals are brought in closer proximity these two carboxylic groups can actually bind like a dentate. So, it is a mostly a bidentate therefore it can easily cleave to the metal ion and as you would see here for iron tridentate iron 2 citrate you can see a complexation of this form and on oxidation it transforms to ion 3 center and this sort of citrate complexes usually brings about a three dimensional network. So, when you have the this sort of complexation in three dimensional picture once you start heating it all these organics will start leaving away and therefore you are essentially leaving a metal oxygen network which is more reactive to form the corresponding oxide. So, that is the philosophy of using citrate ligand because the binding capacity is very high and therefore you can build a three dimensional network of these complexes. . Another example is spinal oxides that is gamma Fe 2 O 3 which is a very popular oxide and usually it is reddish brown in color and gamma Fe 2 O 3 is magnetic although another phase is also magnetic that is magnetite phase that is Fe 3 O 4. Gamma ion oxide is particularly important for recording purposes as you would see here making this sort of needle shape or acicular shaped ion oxide is very very difficult. Therefore, if you are successful then this can find applications in magnetic recording industry. There are other applications of ion oxide apart from the magnetism that it holds it is used in several industries mostly a pigment also, but I will just highlight how simple precursor root can be used for making this compounds. For example, a series of compounds have been reported by Vernacher group and this one is ferrous fumarito hydrogenate in other words use fumaric acid and make complex which will readily form and you can remove the water of crystallization with the hydrogen of crystallization and that is what you call it as ferrous fumarito hydrogenate and similarly you can use succinic acid or malic acid and you can form a series of hydrazine precursors. What is the use these precursors as you would see here the final decomposition temperature is somewhere around 300 that means you can make all this ion oxide precursor below 300 and when you do that the best part is you can stabilize gamma ion oxide and gamma ion oxide incidentally is a low temperature phase and it is a ferromagnetic phase when you try to heat this ion oxide to very high temperature you lose the magnetism therefore gamma ion oxide transforms into a alpha phase and as a result you lose the magnetic property. So, to stabilize this gamma ion oxide you need a chemical root which will stabilize only the low temperature phase. As you see here gamma ion oxide the reported value is very peculiar where you get two X-ray diffraction peaks at 2.95 and 2.78. It can also be in cubic phase where it is again 2.95 and 2.78, but a closely related ion oxide peak is nothing but Fe 3 O 4, but Fe 3 O 4 almost has the same reflection as that of gamma Fe 2 O 3 only thing one peak would miss here and this is the only peak that distinguishes between Fe 3 O 4 and gamma Fe 2 O 3 why it is important because both are magnetic. However, Fe 3 O 4 is actually a black compound so it is easy for us to guess whether it is a Fe 3 O 4 or Fe 2 O 3, but X-ray can be very deceptive. Therefore, the only clue that you get here is this one. So, knowing this particular phase if you follow all the precursors fumaric succinate or malic based precursors you would see here almost all the precursors are showing only selectively gamma Fe 2 O 3 phase. So, this is a very highly selective precursor that can be used for stabilizing only the low temperature phase. If you need high temperature phase then you need to use a different precursor all together. One more thing we need to understand if you are transforming this to a very high temperature then you are actually going to lose the property and alpha Fe 2 O 3 will come and the best way to distinguish alpha Fe 2 O 3 is you will get a peak at 3.66. So, once you know that then you can understand that part of your gamma Fe 2 O 3 has transformed into alpha. So, here is an example where we see a phase can be stabilized only at low temperature and for which you need to take a corresponding precursor. All precursors does not necessarily give the high temperature phase. So, you need to have a mechanism by which you can control the exothermicity. Another example of a perovskite compound as you see here is a metal ion which is actually in the A site and another metal ion is there B these are the dark blue ones which are nothing but your B cation and these are your oxygens in the corners of the octahedra. So, making this compound again is a big challenge I will just leave one example to show how simple precursor can be used for this is a very old paper published in 70s by Bell Labs by Gallagher. I presume that he passed away in the last decade, but one of the finest metal scientists who really worked on a variety of metal oxide systems. One of his paper shows how we can make rare earth ferrite and rare earth cobaltates. This is rare earth ferrite and rare earth cobaltates both have ABO 3 sort of structure and as you will see here they have used cyanate precursors. Take for example, case A is here and this is lanthanum ion hexasino precursors and this precursor seemingly has a correlation to lanthanum cobaltate because they almost are x-ray similar only thing the major peaks in this case in the case of cobalt is split almost all the peaks that you see is split. Therefore, what you assume there is from orthorhombic it is getting transformed to rhombohedral if you have 200 percent peak which is your largest peak that is usually resembling rhombohedral whereas, this is your orthorhombic or tetragonal symmetry. So, you can index this, but what you see here in all these cases you can get x-ray isomorphous pattern. Therefore, you can even make changes between L A F E 1 minus x cobalt X C N 6. This set of mixtures can also be made because you have x-ray similarity. Nevertheless the point I want to make here is even cyanate based precursors can become useful as you would see here that the decomposition is almost over well below 400 degree C and there are no reports where you can find making ABO 3 structures with such fairly low temperatures. So, low temperature process gives you advantage to get finely reactive powders which can be sintered to theoretical density. So, that is the advantage of using low temperature precursors to get this oxides. Some more examples on complex oxides and I will give you some example of how nitrates or hydroxides can be used as a precursor. For example, you take the case of barium B A P B O 3. This is nothing but ABO 3 type of oxide and we can actually build upon this using Rudelson-Pauper series. Rudelson-Pauper series says that with every addition of another barium you go from B A P B O 3 to B A 2 P B O 4 and we can further keep going adding stackings of the A site cation based oxides as inter layers. So, we can build on this sort of systems for example, strontium lead oxide then you can go for another homologous series that is S R 2 P B O 4 and so on. Now, if we know this X-ray similarity of this precursors then you can even make a mixed metal precursor for example, if you look at B A P B O 3, this is your nitrate precursor which is 7.99 and the strontium is 7.824. So, they are having close structural dimension as a result we can use this as a precursor for making the compounds. Only thing is when you use simple precursor sometimes you may not be able to bring down the calcination temperature in that case you have to go for very high temperatures. As you see in this case you have to play around between 700 to 900 degree C to achieve this perovskate compounds. Vidya Sagar and co-workers as early as 84 they have used hydroxides, cyanides and nitrates as precursors to prepare complex metal oxides. I will give you some more example on that for instance if you look at lanthanum hydroxide lanthanum hydroxide and lanthanum hydroxide both are showing same X-ray isomorphous nature and as a result you can try to make lanthanum aluminates. Similarly lanthanum nickel hydroxide lanthanum cobalt hydroxide they all seem to have the same crystal symmetry and this can be usefully transformed into the corresponding perovskates and here again as I showed to you in the view graph of this X-ray data's you can see the nitrate precursors all having same X-ray morphology and as a result a variety of solid solutions can be made mixed metal oxides. I will come to the last example that of solgile chemistry of all the precursors solgile chemistry is still thriving mainly because the although the cost and the stringent requirements for solgile processing is not that simple and it often involves expensive starting materials yet solgile precursors give a lot of advantage. What is the advantage number one it can be used for not just making metal powders but it can be used for making metal oxide films also. So the same precursor in solution form can be decomposed to get powders or it can be decomposed to make films therefore in thin film approach one of the very well studied method from chemical processing is solgile method therefore it is better to understand little bit on how the solgile processing works. Let us look at the definition of what it is an increasingly popular method for producing ceramic powders is solgile processing stable dispersions or salts of small particles are formed from precursor chemicals such as metal alkoxides or other metal organics by partial evaporation of the liquid or addition of a suitable initiator a polymer like three dimensional bonding takes place within the salt to form a gelatinous network or gel and the gel can be dehydrated and calcium to get a intimately mixed ceramic powder so this is nearly a three step process where you have salt formation then you gel it and the gel builds up a three dimensional network on decomposition gives a metal oxide. Solgile route usually can be scalable we can go for bulk quantities as a result this particular cartoon shows how even in a factory or R and D center you can do the scale up and as you see here these are all the setup for solgile process and it is possible for us to get even kilogram quantities. So lab scale process but it can be translated into a log of industrial scalable process the step that is involved in solgile processing as I told you it says three step process first is taking the corresponding metal oxide in a solvent and hydrolyzing this metal alkoxide to get metal hydroxide and this metal hydroxide actually will be a gelatinous precipitate which has to be gelated which means by careful removing of this water molecules it is possible for us to gel it and this gelation sometimes can take even days and therefore you got to be very patient with this gelation process and when the gelation occurs there is a network that is getting formed which is usually a three dimensional network and on carefully removing the solvent then you can actually get the hydroxide particles and heating that further you will get nano crystalline oxides. So if you are looking for very finely divided oxides and of controlled morphology then solgile process is a very good approach. In the next few slides we will see some examples of how we can make such solgile derived powders and films. So in the next slide we see several products can be made metal oxides like zirconia, copper oxide, titanium and as you see here a range of compounds can be made and one of the specialities of this compound is compounds are you can actually control the size such a way to make circular disc for other applications can also be worked out. Therefore it is very important when we try to transcend from a powder to other forms we need to know whether we have a final control on the size dispersion. One of the chief advantage of solgile process is you can control the size so much so that they will be nearly mono sized and as a result sintering of this kind of compounds to make as disc for other applications becomes very useful. In the other precursor cases sometimes the size distribution of the metal oxide particles are very very less and as a result it is not easy to make such compacts and therefore solgile is still being used in industries to make targets these are targets could be used for sputtering or for pulse laser deposition or for MBE sort of applications and solgile is still considered to be the most popular method by which mono sized oxide particles can be made. So with this reference to its application let us see some examples of non aqueous roots to metal oxide nanoparticles using solgile. Why we are talking about non aqueous because once you do it in solution root which involves water then sometimes the end product can have influence because of the water content. Therefore if you can totally make it organic it is much more refined technique than using aqueous root to get this powders. So aqueous solgile chemistry is usually making a molecular precursor and then you try to use reagents to polymerize it and then get the metal oxide network and molecular precursors are mainly metal organic compounds or they are inorganic salts and polymerization as I told you in the previous slide it involves two main process one is hydrolysis and the other one is condensation process. So in the case of hydrolysis you take alkoxide and you hydrolyse you get metal hydroxide metal hydroxide and condensation actually it involves a elimination of a water molecule therefore you will get a metal oxygen framework and that you can build it for making it into a bulk form. Why non aqueous reagents or reaction is advantageous because in the case of aqueous solgile procedures you have problem with fast hydrolysis and sometimes they are very much dependent on pH and the rate of oxidation concentration of anions all this matters in aqueous chemistry. Therefore if you use a non aqueous method for solgile preparation it will be much more viable and last of it as I mentioned you earlier surface adsorbed water has a significant role on the oxide properties therefore it is better to deal with a non aqueous protocol. Non aqueous solgile procedures they can actually overcome several of these disadvantages. For example what set of techniques can be used or combinations we can use we can actually use a metal alkoxide and think of a ether elimination if we can do a ether elimination then we can build a metal oxygen framework or we can try to look for a ester elimination and in such a case you can actually get a metal oxygen framework of this kind or we can go for metal oxide and metal halide under alkyl halide elimination so we can try to distinctly eliminate this again get the metal oxygen framework. So without water we can without hydraulic system we can go for this elimination reactions and we can still bring about the same final product. Halide was actually reported very early as early as 1951 and where they have used silicon tetrachloride and treated with the phenyl ethanol you can get the silica framework. This was one of the best examples of solgile process which was reported and this was picked up in late 70s and 80s solgile became a very good method for making metal oxygen framework or porous metal oxides. This was the first report of a silica gel formation and then we can actually think of making several nano particles with different approaches. One is titanium nano particles as you would see here the nano particles are nearly mono dispersed and of very fine structure and you can also see the lattice fringes of each titanium particle and the broadening of this x-ray clearly shows that they are nano sized in nature. How do we do that? Take titanium chloride it is very important these are very reactive therefore it has to be done in inert atmosphere if you just expose titanium chloride in air it will immediately convert into titanium salt. So, titanium tetrachloride and titanium propoxide if you try to do that then you can get a alkyl halide elimination all you get straight away is titanium and those are very finely divided. So, this is one way that we can prepare a titanium nano particle using a non aqueous solgile route similarly we can actually take other organic compounds like metal copheron complexes of iron, copper and manganese and then try to do a solgile approach you can see here cuprous oxides can be made manganese Mn3O4, gamma Fe2O3 all this can be made but in this case we are not actually using ROH. So, solgile method does not necessarily demand a metal alkoxide you can also start with any other organic precursor zinc oxide nano particles can also be made using solgile route and in this case you can actually take diethyl zinc this is ZnEt2 and try to react it with topo which is a solvent and then one can get zinc oxide nano particles with very good crystallinity. So, this is another approach by which zinc oxide can be made again zirconia this is a very useful high temperature material. How do we make zirconia take zirconial isopropoxide and zirconial chloride if we try to add this again you get the alkyl halate elimination and straight away you can make zirconia. As you would see here each of this is a zirconial particle and they are almost a mono size. So, if you look at the histogram of this you would see a very narrow distribution of the particle size. So, in a very selective way circular with circular morphology you can get zirconia nano particle and not only that you if you look carefully at the x-ray zirconia shows a cubic phase. It is very important to stabilize a cubic phase zirconia under this conditions. Therefore, this is one of a very proven method by which you can make zirconia nano particles, but only thing the handling becomes a problem as I told you all these are very expensive precursors, but if you are looking for mono size dispersions then you have to use costly chemicals. So, that is the stringent requirement in solgill root again titanium nano particles the methodology is the same use titanium chloride and titanium isopropoxide you can see this sort of rod shape nano particles are formed and these are actually formed with the different temperature and the gelation. The gelling time is a kinematic growth approach and therefore, you can actually restrict the gel formation over a period of time and depending on the gel formation you can actually determine the length and breadth of your nano rods. Therefore, this aging gel aging is very important while you transform it into an oxide. So, synthesis of perovskites and related materials in general the synthesis protocol is all procedures are to be carried out in glove box. So, this is one stringent problem and we can actually try to make other combinations like making lithium oxides and lithium oxide or other perovskites we can follow a general protocol where we can mix metal with benzyl alcohol and then react it with this sort of propoxides to get mixed metal oxides and how do we do that if you are wanting to control the size and shape of this crystals general procedure that is suggested is to put it in an autoclave and heat it. I will show you one or two examples of how such mixed metal oxides can be made specially for oxides like perovskites. Take for example, barium is a metal and it is very reactive. Therefore, you need to keep it in a glove box and dissolve it with the benzyl alcohol and once you do that then you can dissolve barium into benzyl alcohol as a clear solution and then you can mix it with titanium propoxide all this has to be done inside the glove box. Otherwise, the exposure of barium to air it will catch fire and titanium will go into T I O 2 missed. Therefore, it has to be handled with care and this is how it will look like barium dissolved in benzyl alcohol initially it looks like this and then it dissolves into a clear solution and this solution has to be mixed with the titanium isopropoxide and this is your autoclave and you can maintain this in a with a pretreatment at 200 degree C you will get a white powder of barium titanate and this is the general protocol that is followed. So, barium titanate if you want start with barium metal mix it with benzyl alcohol and add it to titanium propoxide heat it in an autoclave at 200 degree C you get barium titanate, but the advantage of using this in an alcohol in an autoclave is that you are not only generating a high pressure, but you are also lowering the temperature. So, at high pressure you are able to stabilize all these high temperature phases. So, this is one way a modified high pressure route I will talk to you about the hydrothermal process in the later lectures. Similarly, if you want strontium titanate you have to start with strontium and barium strontium mix it mix it titanates you can do that and again lithium niobate then you start with lithium and you can try to take the corresponding alkoxide. So, this is one way you can try to make this compounds as you would see here lithium niobate shows a very nice crystalline one. Whereas, in the case of titanates these are phase pure, but the broadening X-ray broadening shows that they are really in a nano size and these are all some of the view graphs that I wanted to show just to say what sort of particles that we can get and whether they are crystalline all this can be mapped with the TEM pictures these are the TEM morphology of the particles and in this case lithium niobate gives a polycrystalline ring pattern whereas, barium titanate gives a polycrystalline ring pattern, but not with this dots this shows that the order or the symmetry is distorted little bit whereas, in this case you can see that the powders are nearly amorphous they have just started crystallizing. So, all these information you can get from the TEM picture and we can also make simple oxides take benzyl alcohol and put vanadyl isopropoxide in an autoclave then you can get vanadium oxide, niobium oxide, tarantula moxide, indium oxide all this can be done with the precise control on the geometry and shape of these particles as you would see the X-rays are very clearly showing that and you can also find out at low temperature when you heat the samples they are amorphous in nature, but they crystallize when you take it to high temperature. These are the TEM characterization results which shows that sol-gel process has a size and shape control therefore, you can see tantalum oxides very nice lattice fringes of this is seen and you know almost all cases you would see a polycrystalline feature and here you can see square or rod ship particles here again V2O3 particles are agglomerated and similarly we can show tin oxide, tin indium oxide and nice indium oxide particles can be formed using TEM. So, in brief sol-gel process can be a very useful method for precursors these systems bear a very high potential for making high purity metal oxides via soft chemistry route and therefore, among the precursor roots sol-gel precursor route is one of the very coveted and more used method. The reactions are simple easy to scale up and they form highly crystalline nano powders, nano particles in form of powders are highly decided for applications as a result sol-gel can be used for scaling up operations. To sum up on these two lectures on precursors I just want to make two comments one is precursor roots therefore, range from simple to complex mechanism and procedures. So, as you saw examples of simple precursors like nitrates, hydroxides something some of these can have x-ray similarity we can widen the scope of solid solutions, but usually they are cheaper and therefore, you can try to make the corresponding oxides at a fairly low temperature, but when you look for high purity and mono size and lot of others stringent requirement on your final products you need to go for sophisticated methods, but there are given taking in each approach. So, there are certain things that the sol-gel chemistry approach lacks which you can take it from simple precursor roots and as I told you solid solution precursor root is one of the other approach which really stands up, but then there again there may be compromise in the issue of the final properties. So, precursor roots can give us a lot of dimension to making new metal oxides there may be some phases which may not be known, but precursor roots can help us understand and help us synthesize such new stratometries or new phases mainly because what is achieved at high temperature can be realized at low temperature as a result it provides a new pathway to stabilize metastable phases also. So, we need to take all these issues into consideration when we try to look at making new stratometries and new metal oxide combinations.