Theoretical and practical advances in the field of ferroelectcitricity stimulate search for, as well as preparation and investigation of, novel ferroelectrics exhibiting high pyroelectric, electric, optical and mechanical characteristics. This situation necessitates systimatization in analysis of available experimental data on various types of novel ferroelectric materials. A unique crystalline structure and an interesting complex of physical properties are displayed by the group ABO4 compounds (A = Sb or Bi, and B = Nb, Ta or Sb+5) belonging to the stibiotantalite type of structure.Of scientific and practical importance is the investigation of the advantageous effect exerted by dopants on principal electrophysical characteristics of group ABO4 compounds.

Kristall und TechnikVolume 14, Issue 5 p. 509-525 Übersichten Hydrothermal synthesis of crystals† Dr. L. N. Demianets, Dr. L. N. Demianets Shubnikov-Institute of Crystallography, Academy of Sciences of the USSR, Lenin Prospect, 59 117333 Moscow, USSRSearch for more papers by this authorDr. A. N. Lobachev, Dr. A. N. Lobachev Shubnikov-Institute of Crystallography, Academy of Sciences of the USSR, Lenin Prospect, 59 117333 Moscow, USSRSearch for more papers by this author Dr. L. N. Demianets, Dr. L. N. Demianets Shubnikov-Institute of Crystallography, Academy of Sciences of the USSR, Lenin Prospect, 59 117333 Moscow, USSRSearch for more papers by this authorDr. A. N. Lobachev, Dr. A. N. Lobachev Shubnikov-Institute of Crystallography, Academy of Sciences of the USSR, Lenin Prospect, 59 117333 Moscow, USSRSearch for more papers by this author First published: 1979 https://doi.org/10.1002/crat.19790140503Citations: 6 † Paper presented on the 13. Annual Meeting of the Vereinigung für Kristallographie November 14–17, 1978 in Frankfurt/Oder, GDR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume14, Issue51979Pages 509-525 RelatedInformation

The growth mechanism of the early formation stages of sodalite single crystals grown by the method of hydrothermal synthesis on single crystal seeds coated with interfacial layers of polycrystalline silver has been studied at an electronmicroscopic scale. Coating with interfacial layers leads to a very weak adhesion between the overgrown single crystal and the surface of the interfacial layer on top of the seed, thus providing a unique possibility of detaching the overgrown single crystals from seeds and investigating the very early crystallization stages by the morphology of the growth surface. In local microregions of seed surfaces coated with interfacial layers discrete particles arise differing from one another in morphology, this being primarily associated with the electrical heterogeneity of seed surfaces. During crystallization, the space between the discrete particles was filled with the hydrothermal solution which represented a liquid interfacial layer exhibiting informative properties occurred under the influence of electrically active elements of the seed surface. At the boundary separating the liquid interfacial layers with particular informative properties from the rest of the solution volume, at early crystallization stages, together with the formation of discrete particles directly on the coated seed surface, growth of a continuous sodalite single crystal took place. The informative properties of seed surfaces, which are regularly modified due to coating with interfacial silver layers, determine the occurrence on local regions of seed surfaces (under appropriate crystallization conditions) of one or the other polymorphous modification: either hexagonal – cancrinite, or cubic – sodalite.

The conditions of growth of the SbNbO4, SbTaO4 single crystals on seed were studied by the hydrothermal method. Growth took place at the temperatures 490–530°C in the dissolution zone, the temperature drop being 40°C and the pressure 1500–1700 atm. We found that SbNbO4 single crystals were excellently activated by different elements. The temperature dependence of ε for SbNbO4, activated by Co, Fe, Pb, Sn, Ti was studied. In the course of the work Pb5S2I6 single crystals were synthesized. The temperatures of phase transitions for single crystals Pb5S2I6 are about 300°C.

Sodium cobalt germanate Na2CoGeO4 single crystals were grown by different techniques under hydrothermal conditions. Peizoelectric, elastic and dialectric properties of these crystals were investigated. The sound velocities varied from 4.4 to 5.8 × 105 cm/sec for longitudinal waves and from 2.1 to 3.2 × 105 cm/sec for shear waves. Maximal electromechanical coupling factor was 25%. All independent components of tensors of piezoelectric, elastic and dielectric constants, and elastic and piezoelectric modules were determined.

The latest results such as (1) the discovery of a multitude of “critical” points for some compounds of this family, (2) the structure of ferroelectric, antiferroelectric and paraelectric phases of SbNbO4 in the interval 25–700°C and (3) the properties of the doped monocrystals of SbNbO4 are given below.

Large single crystals of Na2CoGeO4 were grown under hydrothermal conditions. Two methods are used: crystallization on seed and spontaneous growth in temperature gradient conditions. The comparison of the defect distribution shows the best quality for crystals obtained with the most rapid growth rates.