Peculiarities of the crystallization process and growth of pure nonstoichiometric ZnMoO4 single crystals and those doped with WO3

Abstract

200 g ZnMoO₄ single crystals, both pure and doped with WO₃, were grown from appropriate powder mixtures of oxides via the low-temperature gradient Czochralski technique, and plates cut from them were characterized in detail. The crystal-chemical formulas of non-stoichiometric Zn_1.010Zn_yMo_1−yO_1.010+3−2y (y = 0.007) crystals, being substitutional solid solutions with ionic defects, such as Zn_Mo⁴⁻, V_O²⁺, and Zn_i^2′, were established based on determination of the compositions, densities and lattice unit cell parameters with very high accuracy. This characterization allowed for clarification of the role played by each stage of crystal growth, including solid-phase powder synthesis, high-temperature homogenization and crystallization, which proceeded sequentially in one reactor that was semi-open to the air. It was shown that MoO₃ volatility is the primary source of issues. The first stage, resulting in a non-equilibrium grain-zoning product, was the key to creating MoO₃ vapor pressure in the reactor and a melt composition enriched by the ZnO component. The conditions for the stable crystallization of nonstoichiometric crystals were determined. The experimentally observed shifts in the characteristic liquidus and solidus temperatures of non-stoichiometric ZnMoO₄ crystals doped by WO₃ were found to be of importance to minimize the negative effects of peritectic melting.