To achieve good quality bulk size crystal growth, an assessment of the nucleation kinetics of a semi‐organic L‐leucine hydrobromide (L‐LHBr) crystal was carried out using double‐distilled water as solvent medium. The effect on metastable zone width (MSZW) with increasing temperature and on induction period with varied supersaturation level was determined experimentally and was found to be very well in accordance with the nucleation theory prospects. Thereafter, various other nucleation parameters, such as Gibbs free energy and interfacial energy, were also determined. The knowledge of these nucleation parameters indicated the requisite temperature domain and the appropriate growth technique, leading to the successful single‐crystal growth of L‐LHBr by slow cooling in the temperature range 298–291 K. The cooling rate of 0.25 K per day was optimized after repeated trials. X‐ray diffraction and Raman analysis were performed on grown crystals for the verification of the material. High‐resolution X‐ray diffraction analysis was used to assess the crystalline perfection of the grown crystals. To further explore the properties of the grown crystals, photoluminescence and time decay studies, etching analysis, and Z‐scan measurements were performed.

As‐grown and chemically reduced Rh‐doped (1500 p.p.m.) KnbO3 single crystals grown by the Czochralski method have been characterized. Reduction of the grown crystals at different levels was carried out under a mixture of CO and CO2 gases as the crystals were grown with excess oxygen. The effect of reduction and poling on crystalline perfection was studied by high‐resolution X‐ray diffraction (HRXRD) using a multi‐crystal X‐ray diffractometer developed in‐house. The diffraction curves of the as‐grown, electrically poled, moderately reduced and heavily reduced single‐crystal specimens show remarkable differences. The studies by HRXRD reveal that poling has some influence on the improvement of crystalline perfection, while chemical reduction has a great influence on crystalline perfection; at moderate reduction the crystal becomes nearly perfect, but when the reduction is very heavy the crystal quality decreases slightly, although it is still better than for unreduced samples. Asymmetry of the diffraction curves with respect to the peak position reveals that the as‐grown specimens contain a high concentration of both vacancies and self‐interstitials. After poling, the concentration of self‐interstitial defects is lowered to some extent. When the specimen is moderately chemically reduced, the scattered intensity on both sides of the peak is greatly reduced, showing that the concentrations of both vacancies and interstitials are reduced to a great extent owing to chemical reduction. This clearly indicates that, as a result of the chemical reduction of oxygen in the crystal, crystalline perfection is enhanced significantly. However, under heavy chemical reduction, the number of vacancy defects is increased to a significant extent. Raman scattering, dielectric and photoluminescence studies also show interesting features, with excellent correlation with the degree of crystalline perfection influenced by the processes of reduction and poling.