Dislocation activity in single crystals of stannic iodide

Single crystals of stannic iodide (SnI₄) have been grown employing the controlled-reaction between SnCl₂ and KI solutions by diffusion process in silica gels. As-grown (111) surfaces of the crystals have been optically studied. Characteristic growth spirals and hopper growth patterns have been observed on them. By successively etching (111) surfaces in a 0.2 N HCl solution, it is established that the pits indicate the sites of dislocations in the crystals. This is further confirmed by comparing the etch patterns before and after chemically polishing (111) surfaces. The average dislocation in the SnI₄ crystals have been determined and found to be 7.3 × 10² cm⁻². Observations of polygonisations are described and the implications are discussed.     

Effect of heat treatment on the optical absorption of tin diselenide thin films

Optical absorption measurements were made on tin diselenide thin films grown on glass substrates by thermal evaporation of stoichiometric bulk compound. In the as-deposited films, optical absorption was dominated by an indirect transition at lower photon energies with a band gap of 1.4 eV. The direct allowed transition with a band gap of 1.62 eV was predominant at higher energies. Annealing the film at elevated temperatures resulted in the decrease of both the direct and indirect transition band gaps.     

Change in morphology and dislocation Etch Pits on the (010) Surface of Magnesium Orthosilicate Crystals

Investigations made on the etching behaviour of magnesium orthosilicate crystals in hydrochloric acid and melts of potassium and sodium hydroxides are described. It is shown that the morphology and orientation of the etch pits depend upon the concentration, composition and temperature of the etchant used. At low concentrations of HCl acid solution, the boat shaped pits produced are oriented along [100] direction while in concentrated acid, the hexagonal pits produced are oriented along [001] direction. At intermediate concentrations of about 5 N HCl acid the pits are square. KOH melt at 400 °C is found to produce rectangular pits with their longer sides parallel to [100] direction. The effect of a mixture of KOH and NaOH in different proportions in the melt is investigated. It is observed that square pits are obtained in melt of the mixture of KOH and NaOH in the proportion of 6:4 respectively. The mechanism responsible for the change in orientation of etch pits have been explained. The implications are discussed.     

Electrical conduction in ferroelectric lead hydrogen phosphate single crystals

Single crystals of LHP (Lead Hydrogen Phosphate) have been grown using the controlled reaction between lead nitrate and orthophosphoric acid solution by diffusion process in silica gel medium. Transparent crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The d.c. electrical conductivity of both single crystals and pelletized samples of LHP have been studied in the temperature range from 313 to 968 K. It has been observed that: (i) the d.c. conductivity of the crystalline sample is greater than that of thepellet sample, (ii) three distinct electrical conductivity processes have been observed and are interpreted as extrinsic, intrinsic, phase changes, and (iii) the activation energy for the conduction in the crystalline sample is greater than that of the pellet sample. The magnetic susceptibility measurements reveal that the paramagnetic characteristic of these materials and the implications are discussed.