Vapor Growth of Zn₂GeO₄ Needle Crystals

Abstract

Needle crystals of Zn₂GeO₄ were obtained by heating the mixed powder of 2 ZnOGeO₂*(0.5 g) with graphite powder ( 0.0 5-0.5 g) in a polcelain crucible at 1000-1100°C for 20 minutes.
The crystals are colorless and transparent whose width and length are 20-40 dua nd 7- 15 mm, respectively. The growth direction is along chexa xis. The lattice constants are ah_max = 14.23₂Å, chex=9.52_ηÅ.
Zn₂GeO₂ p owder is immediately produced from the starting mixture. of ZnO and GeO₂ at an elevated temperature. Upon reduction of Zn, GeO, with graphite powder, vapor of Zn and Ge0 with the ratio of 2: 1 evolves in a crucible. Vapor of Zn and GeO reacts again w ith oxygen to produce Zn₂GeO₄ crystals according to the following equation: 2Zn GeO+ 3/2 O₂→ Zn₂GeO₄.
Under the optimum condition (graphite powd er: 0.25 g, temp.: 1050°C) for the crystal growth, the formation rates of vapor of Zn and Ge0 are 3.6 x 10^-6 mot/sec and 1.8 X 10^-6 moli sec, respectively. The crystals grow upon reaction of these vapor species with oxygen in an air introduced into a crucible through a space between it and its lid. The flow rate of oxygen into a crucible was determined as 3.5-7.0 x 10^-6 mol/sec from the weight loss of contents in the crucible. The crystals probably grow under the excessive supply of oxygen.