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The main processes for preparing bulk single crystals and films of photorefractive and piezoelectric Bi 12 M x O 20 ± δ (M = Group II-VIII elements) sillenite compounds are considered. Experimental data are summarized on the crystal growth of Bi 12 M x O 20 ± δ from the melt and under hydrothermal conditions, and the key morphological features of sillenites are analyzed. Various types of macroscopic growth defects in sillenite-type crystals are described, and their origin is discussed. The compositions of second-phase inclusions in undoped and doped (Group I-VIII elements) Bi 12 SiO 20 , Bi 12 GeO 20 , and Bi 12 TiO 20 single crystals are presented, and the main physicochemical properties of various Bi 12 M x O 20 ± δ crystals are summarized.

Experimental data are presented and available published information is generalized on phase rela tions in the Bi 2 O 3 -TiO 2 system. The phase diagrams in stable equilibrium and metastable states are con structed. The homogeneity range of the phase with a sillenite Bi 12 TiO 20 structure is refined, and so is the tem perature range of the existence of the metastable and equilibrium states of the phase with a pyrochlore Bi 2 Ti 2 O 7 structure.

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