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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.

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Ala evidence that local ordered magnetic fields from 30 to 200 G exist in diamagnets ct-Bi203, Bi304Br, Bi4Ge3Oi2, Bi2AI409 which comp¡ neither d-nor f-elements was earlier given by the zerofield and Zeeman-perturbed 2~ nuclear quadrupole resonance (NQR) spectra. With a view to fmd similar spectroscopic effects in other compotmds, we examined the 2~ NQR Zeeman-perturbed spectra of the Bi3BsO~2 oriented single crystal as well as the zero-field spin echo envelopes in Bi3B50~2 and Bi2Ge309. Distinctive modulations were displayed by the zero-field 2~ spin echo envelopes in Bi2Ge309 powder. The modeling of the spin echo envelopes within the density matrix formalism explained the observed effect by the presente of local ordered magnetic field of the order of 65 G at the Bi atoms. The zerofield modulations of the Z~ spin echo envelopes were also observed in Bi3B5OI2 indicating the presence of the internal source of line splitting. This finding and considerable deviation of the resonance intensity ratios from that in a pure NQR, found in the zero-field 2~ spectrum of the single crystal, were understood as indirect evidences that a local ordered magnetic field exists also in Bi3BsO12. The zero-field 2~ spin echo envelopes assigned to the lines split by the local magnetic fields in a-Bi203 and Bi4Ge3Ot2 were observed to display modulations on the appropriate curves.