U. V. Subba Rao

Microhardness studies in alkali halide mixed crystals

Microhardness measurements done in KCl, KBr and in different compositions of KCl-KBr mixed crystals show that it varies nonlinearly with composition. In order to investigate the nature of defects, several techniques such as etching, ionic conductivity and dielectric loss have been employed which showed that the mixed cristals of KCl-KBr are more defective, containing a high concentration of dislocations, low-angle grain boundaries and vacancies as compared to the end products KCl and KBr. These imperfections appear to be responsible for the nonlinear variation of microhardness in mixed crystals. The microhardness studies also revealed that the difference in size of the ions constituting the mixed system are responsible for the internal strains which in turn give rise to imperfections affecting the microhardness of mixed crystals.

Growth and characterization of alkali halide mixed crystals

Abstract The study of the physical properties of alkali halide mixed crystals has been a subject of wide interest in the recent past. The main aim of this review is to provide a survey of the current state of knowledge about the nature of imperfections present and their role in understanding various properties associated with alkali halide mixed crystals. An attempt has been made to distinguish different types of mixed crystals, the conditions for the formation of a mixed crystal, the local strains that arise in the lattice due to the difference in the size of the ions that constitute the mixed crystal. The results obtained from various studies such as ionic conductivity, dielectric loss, microhardness, radiation hardening, colour centres, thermoluminescence, optical absorption etc. on alkali halide mixed crystals are presented. The non-linear variation of electrical conductivity, microhardness, half widths of many colour centre bands with composition have been discussed in terms of the concentration of various defects present in them. The aspects of the problem described include: 1. a) Dislocation density and distribution studies. 2. b) Influence of dislocations and grain boundaries on transport properties of these crystals. 3. c) Role of ionic size on microhardness. 4. d) Lesser rate of hardening in mixed crystals due to irradiation. 5. e) Stability of colour centres in mixed crystals in comparison with the end products, finally the present position and out look are summarized.

Electrical breakdown studies in didymium oxide thin films

Abstract I–V characteristics of sandwiched Al-didymium oxide-Al structures are studied for different thicknesses. The breakdown voltage increases and the dielectric strength decreases with increase of film thickness. Optical photomicrographs of the breakdown patterns during different stages of dc voltage are taken and the results discussed.

On the thermoluminescence of X-ray irradiated polycrystalline NaYF4 powder

Utilisation des spectres de thermoluminescence pour etudier les centres colores formes par irradiation RX

Z2 centres in NaCl crystals doped with gadolinium

Etude de la formation des centres Z 2 dans des echantillons NaCl dopes par Gd 2+ et irradies aux rayons X, a partir des courbes de thermoluminescence