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Results of X-ray diffraction, dielectric, and Raman studies of the ferroelectric Li0.125Na0.875NbO3solid solution obtained under hot-pressing conditions (6 GPa, 1400 and 1800 K) are compared with those of the same compound synthesized by conventional ceramics technology. The thermo-barometric synthesis is found to improve the ordering of cations and to increase the value of dielectric permittivity and ion conductivity of the ceramics. [ABSTRACT FROM PUBLISHER]

The structure of LiNaTaNbO ceramic solid solutions and the processes of its disordering with a change in composition and temperature have been studied by full-profile X-ray diffraction analysis and Raman spectroscopy. It was established that at room temperature the structure of LiNaTaNbO solid solutions is close to the NaNbO structure and has a space group P21 ma with four formula units per unit cell. It was shown that the oxygen octahedra in the LiNaTaNbO solid solutions (0, 0.15, 0.03, 0.04, 0.05) are slightly distorted and their geometry is identical to that of octahedra in the NaNbO structure. The temperature dependence of the intensities of lines in the Raman spectrum of LiNaTaNbO solid solutions corresponding to vibrations of Li and Na cations in the cuboctahedral structural voids revealed a strong disordering in the alkali metal sublattice at a temperature above 322°C. This may indicate the essential stepwise increase in the Li cation mobility and may result in a change in the kinetic and energetic characteristics of ion charge transport. [ABSTRACT FROM AUTHOR]

The structure of ceramic solid solutions LiNaTaNbO has been investigated by full-profile X-ray diffraction analysis and Raman spectroscopy. It is shown that their structure for all x values is similar to the NaNbO structure. The structure of NaTaNbO solid solutions ( x = 0) is characterized by the sp. gr. Pbcm, and the structure of LiNaTaNbO solid solutions with x = 0.05, 0.1, and 0.16 is characterized by the sp. gr. P2 ma. The unit-cell parameters decrease with an increase in x. At x = 0, doubled values of the parameter c and, correspondingly, the unit-cell volume are observed in the antiferroelectric phase. This fact is confirmed by the form of the vibrational spectrum in the region of stretching modes of oxygen atoms along the polar axis. [ABSTRACT FROM AUTHOR]

Experimental data demonstrate that LiNaTaNbO ( y ≠ 0) ferroelectric solid solutions near special concentration points ( x = 0.125 and 0.25), which have increased degrees of short- and long-range order, undergo a superionic transition. In the Raman spectra of LiNaTaNbO, the superionic transition shows up as a predominant 'melting' of the alkali metal sublattice and broadening of the corresponding lines into a Rayleigh line wing, whereas the other sublattices in the structure remain relatively 'rigid.' The temperature of the superionic transition can be tuned by varying the degree of static disorder of structural units in the Nb/Ta sublattice. [ABSTRACT FROM AUTHOR]