Question

Synthesis of crystalline materials is greatly facilitated if the reaction mixture is homogeneous on an atomic scale. Describe some (at least three) of the routes that could be used to synthesise a sample of BaTiO3 powder and compare the advantages/disadvantages of each. Describe the strategies that can be adopted to synthesise thin films of semiconductor materials such as CdS or GaAs.

Answer 1

First Route: Hydrothermal Synthesis

Starting Material: Water soluble Ba(OH)₂. 8H₂O and insoluble TiO₂ powder

Procedure: These two materials are mixed in an aqueous solution kept at a temparature near it's boiling point near it's boiling point for prolonged times.

Second Route: Molten salt synthesis methods

starting material: BaCO₃, TiO₂, NaCl, KCl,

procedure: BaCO₃ and TiO₂ powders were mixed with eutectic composition of NaCl-KCl in their molar ratio. Isopropyl alcohol was used for making the homogeneous mixture with these powder mixture. The mixture was heated at 700-800⁰ C upon alumina crucible.Then the powders were washed with hot deionized water until no Cl^- ion. The powders were again dried in an oven at 100⁰C.

Third Route: Soft Chemical method

Reagents: Ba(NO₃)₂, TiO(NO₃)_{2 ,} nitric acid, Tartaric acid, ammonium nitrate

procedure: Ba(NO₃)₂ solution and TiO(NO₃)₂ solution were dissolved in nitric acid. Tartaric acid solution was then added to the resulting solution. The solution was then heated until all the liquid evaporated. Solid ammonium nitrate was added towards the end to heating procedure avoid slurry formation.This fine powder was dried on a hot plate at 130 °C for 30 min.

advantages :

Hydrothermal Synthesis: synthesize materials below a transformation temperature, transition metal compounds may be synthesized with unusual oxidation states

Molten salt synthesis (MSS) : cost effectiveness, easy setup, low temperature synthesis and controllable size of products.

softchemical method: superior control over size, shape, and surface functionality

Preparation of synthesis of thin film of CdS by Chemical Bath deposition method:

step 1.Cadmium nitrate and thiourea were taken in an alkaline solution of ammonia and distilled water.

step 2. Cleaned (using acetone by ultrasonically) Commercial glass slides used as substrates

step 3. This glass slides shoul kept vertically in a closed beaker containing distilled water and cadmium nitrate was added along with liquid Ammonia.

step 4. Mixture was then stirred and thiourea was added to it.

step 5. Glass substrate was pull out vertically on the beaker containing the solution.

step 6. After that, the substrates were removed from the bath and were allowed to dry in air.

step 7. The prepared samples were rinsed with acetone and finally dried.