• D B Sirdeshmukh

Articles written in Bulletin of Materials Science

• Systematic hardness studies on lithium niobate crystals

In view of discrepancies in the available information on the hardness of lithium niobate, a systematic study of the hardness has been carried out. Measurements have been made on two pure lithium niobate crystals with different growth origins, and a Fe-doped sample. The problem of load variation of hardness is examined in detail. The true hardness of LiNbO3 is found to be 630 ± 30 kg/mm2. The Fe-doped crystal has a larger hardness of 750 ± 50 kg/mm2.

• Systematic hardness measurements on some rare earth garnet crystals

Microhardness measurements were undertaken on twelve rare earth garnet crystals. In yttrium aluminium garnet and gadolinium gallium garnet, there was no measurable difference in the hardness values of pure and nominally Nd-doped crystals. The hardness values were correlated with the lattice and elastic constants. An analysis of hardness data in terms of the interatomic binding indicated a high degree of covalency.

• Systematic hardness measurements on CsCl𝑥Br(1–x) and NH4Cl𝑥Br(1–x) mixed crystals

Vickers hardness measurements have been made on polycrystalline blanks of CsCl𝑥Br(1–x) and single crystals of NH4Cl𝑥Br(1–x). The composition dependence of hardness is highly nonlinear in both systems and follows an empirical model that includes a lattice contribution and a disorder contribution. The Gilman–Chin parameter (𝐻/𝐶44) has been calculated and its significance discussed.

• Systematic hardness measurements on single crystals and polycrystalline blanks of cesium halides

Vickers and knoop hardness measurements were carried out on CsBr and CsI single crystals. Polycrystalline blanks of CsCl, CsBr and CsI were prepared by melting and characterized by X-ray diffraction. Vickers hardness measurements were carried out on these blanks. The hardness values were correlated with the lattice constant and the Schottky defect formation energy.

• Systematic hardness measurements on mixed and doped crystals of rubidium halides

Efforts are made to improve the hardness of rubidium halide crystals by

solid solution hardening and

impurity hardening.

Systematic microhardness measurements have been made on rubidium halide mixed crystals (RbBr–RbI and KI–RbI) and rubidium halide crystals doped with Sr2+ ions. The composition dependence of the hardness of mixed crystals follows the law $\Delta H_V$ = $K\ x$ (1–𝑥), where $\Delta H_V$ is the enhancement in hardness, 𝐾 a constant and 𝑥 and (1 – 𝑥) the concentrations of the first and second component of the mixed crystals, respectively. The hardness of doped crystals increases with the concentration 𝐶 of the dopant according to the law, $\Delta H_V$ = $k\ C^m$, where 𝑘 and 𝑚 are constants. The relative efficacy of the two methods of hardening is discussed.

• # Bulletin of Materials Science

Volume 44, 2021
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020