Calcium germanate

Description

Calcium germanate can be formed by firing the oxides together at about 750–800°C:
CaO + GeO2?CaGeO3
A single-crystal X-ray study indicates that the perovskite form of CaGeO3 is orthorhombic (Pbnm) and isotypic with GdFeO3. The cell dimensions are: a = 5.2608 ? , b = 6.2688 ? , c = 7.4452 ? , V = 366.43?³, Z = 4, dcalc = 5.17 g/cc. The crystal structure is close to that of SmAlO3. Although the unit cell of CaGeO3 is pseudocubic, the structure itself is very distorted through the tilting and distortion of polyhedra. The oxygen polyhedra are less tilted and less distorted than those of other GdFeO3-type perovskites.

Physical properties

By using a diamond anvil pressure cell coupled with laser heating, Ca2GeO4 has been found to decompose into the mixture Ca3Ge2O7 plus CaO at pressures greater than 200 kbar and at about 1000°C.

Uses

Ca2GeO4 has been tested as a host for lasers, using Nd³⁺ as the activator. Large crystals of highly doped Ca2GeO4:Cr⁴⁺ were grown by a top-seeded meltsolution growth method. Absorption and emission measurements for various crystal orientations have been performed.