Crystal growth, structure, and physical properties of Bi2Ge3O9

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Abstract
Single crystals of Bi2Ge3O9 of optical quality with dimensions of approximately 15×15×50 mm3− have been grown by the Czochralski technique from a stoichiometric melt. The space group is P 63/m, Z = 2, a 1 = 0.7006 nm, a 3 = 0.9786 nm. The structure (R = 0.052) is closely related to that of benitoite. Trigermanate rings are located in planes perpendicular to the six-fold axis. The elastic and thermoelastic constants, the indices of refraction, and the coefficients of thermal expansion have been measured. The elastic properties reveal strong covalent bonds which are assigned to the trigermanate rings. Thermal expansion parallel to the six-fold axis is extremely small. The crystals are potentially feasible for X-ray spectrometer applications and photoacoustic deflector devices.