K Kishan Rao
Articles written in Bulletin of Materials Science
Volume 23 Issue 2 April 2000 pp 147-150 Mechanical Properties
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.
Volume 24 Issue 5 October 2001 pp 469-473 Crystal Growth
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.
Volume 24 Issue 6 December 2001 pp 665-669 Single Crystals
Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (111) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.
Volume 25 Issue 7 December 2002 pp 641-646 Mechanical Properties
Single crystals of NaClO3 and NaBrO3 are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO3 whereas in addition to the cracks at the corners microcracks also appeared in NaBrO3 crystals around the impressions. The impressions formed in NaBrO3 are not very clear as in NaClO3, a possible mechanism for it is discussed. The work hardening index number (𝑛) for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO3 is harder than NaClO3 (𝛥 𝐻 ≈ 100 kg/mm2), this could be due to strong inter ionic forces acting between Na–Br in NaBrO3 crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (𝐶44) and are found to be close to the experimental results.
Volume 29 Issue 5 October 2006 pp 427-432 Single Crystals
A study of growth rates of NaClO3 and NaBrO3 has been carried out using a small growth cell by
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