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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 LiNbO 3 is found to be 630 ± 30 kg/mm 2. The Fe-doped crystal has a larger hardness of 750 ± 50 kg/mm 2 .

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.

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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.

A study of growth rates of NaClO 3 and NaBrO 3 has been carried out using a small growth cell by in situ observation. Normal growth rates of {100} faces of NaClO 3 and {111} faces of NaBrO 3 along 〈 〈110〉 〉 direction are measured under relatively high supersaturation ranging from 3-8%. In the initial stages of growth, {100}, {110} and {111} faces develop in NaClO 3 and gradually all the faces are replaced by the {100} faces only. In the case of NaBrO 3 , mostly {111} faces develop with occasional occurrence of small {100} faces at the intersection of {111} faces. The growth mechanisms are investigated from growth rate vs supersaturation plots and from the observations of surface features. In the present supersaturation range, the growth mechanism appears to be due to two-dimensional growth mechanism.

Single crystals of NaClO 3 and NaBrO 3 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 NaClO 3 whereas in addition to the cracks at the corners microcracks also appeared in NaBrO 3 crystals around the impressions. The impressions formed in NaBrO 3 are not very clear as in NaClO 3 , 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 NaBrO 3 is harder than NaClO 3 (∆ ∆H ≈ ≈ 100 kg/mm 2), this could be due to strong inter ionic forces acting between Na-Br in NaBrO 3 crystals. Using Gilman's empirical relation, hardness values are calculated from the values of elastic constants (C 44) and are found to be close to the experimental results.

Solubility equilibria of hydroxylapatite, chlorapatite, and a series of their solid solutions were investigated at 37 °C in the pH range 4.25 to 7.40 and their solubility products evaluated. Proof could be obtained for their stoichiometric dissolution.