I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Material KSC RAS, Apatity, Russia:

M. N. Palatnikov, Sector Leader
O. B. Shcherbina, Senior Researcher, e-mail: shcerbina@chemy.kolasc.net.ru
S. M. Masloboeva, Assistant Professor
V. V. Efremov, Senior Researcher

The structure, mechanic and electric properties were researched in ceramics obtained on the basis of highly disperse microcrystal single phase powders of lithium niobate. Methods of research were probe microscopy and impedance spectroscopy. The distribution of powder particles sizes was narrow. The ceramic materials properties was shown to depend on dispersity of the initial powder lithium niobate charge. At this, due to formation of gradient mezostructure in LN ceramic obtained from initial charge with low specific surface area microhardness measured on the surface of this sample was almost equal to the one of samples more homogeneous in size grains and more dense synthesized from charge with higher specific surface area. At the same time Young modulus that is a strength index of the material, is naturally higher for LN ceramic samples obtained from charge with higher specific surface area. Great differences in ceramic structure on mezo- and microlevels manifest in mechanical properties especially in the destruction processes and strength. The criterion for evaluation of plastic and brittle properties was chosen micro-brittleness and brittle microstrength. The obtained data allowed us to evaluate critical stress intensity factor of the first kind K_IC which is a material crack-resistance criterion. Crack-resistance and microhardness of the materials were shown to increase with increase in the dispersity of the initial charge. The dispersity of complex impedance Z*(ω) was researches for the most dense LN ceramic sample in the temperature range up to ~800 К. Real and imaginary components of the complex dielectric permittivity and complex impedance (admittance) were detected due to measured real value of impedance (Z) and phase difference angle (φ). Temperature dependence of static conductivity σ_sv(Т) of LN ceramic agrees with the Arrhenius law only in hightemperature area. The dependence has a monotonous shape with activation enthalpy Н_а≈0.88 eV. Such value is typical for the ion conductivity along the ceramic grain boarders. Comparison of the specific static conductivity of ceramic and crystals LN samples revealed that ceramic conductivity is four times of magnitude higher σ_sv~5.0·10^–8 S/m and 5.0·10^–12 S/m, correspondingly.

1. Kühler M., Fritzsche W. Nanotechnology: An Introduction to Nanostructuring Techniques. Weinheim : Wiley-VCH. 2004. pp. 27–28.
2. Masloboeva S. M., Palatnikov M. N., Arutunjan L. G. et al. Obtaining and investigation of microcrystalline powders of lithium niobate and tantalate. Collection of scientific proceedings “Physical and chemical aspects of investigation of clusters, nanostructures and nanomaterials”. Tver : Tverskoy Gosudarstvennyy universitet. 2016. Iss. 8. pp. 239–246.
3. Bulanov V. Ya., Kvater L. I., Dolgal T. V. et al. Metallic powder diagnostics. Moscow : Nauka, 1983. 280 p.
4. Palatnikov M. N., Sidorov N. V., Kalinnikov V. T. Segneto - electric solid solutions based in oxide compounds of niobium and tantalum. Saint Petersburg : Nauka. 2002. 304 p.
5. Oliver W. C., Pharr G. M. An Improved Technique for Determining Hardness and Elastic Modulus Using Load and Displacement Sensing Indentation Experiments. Journal of Materials Research. 1992. Vol. 7. pp. 1564–1583.
6. Useinov A. S. A Nanoindentation Method for Measuring the Young Modulus of Superhard Materials Using a NanoScan Scanning Probe Microscope. Pribory i tekhnika eksperimenta. 2004. No. 1. pp. 134–138.
7. Tsai Y.-T., Whitmore D. H. Nonlinear Least-Squares Analyses of Complex Impedance and Admittance Data for Solid Electrolytes. Solid State Ionics. 1982. Vol. 7. pp. 129–139.
8. Jonscher A. K. Dielectric Relaxation in Solids. Chelsea Dielectrics Press. London. 1983. 380 p.
9. Yatsenko A. V., Palatnikov M. N., Sidorov N. V., Pritulenko A. S., Evdokimov S. V. Specific features of electrical conductivity of LiTaO₃ and LiNbO₃ crystals in the temperature range of 290–450 K. Physics of the Solid State. 2015. Vol. 57, No. 8. pp. 1547–1550.
10. Akhmadullin I. Sh., Golenishchev-Kutuzov V. A., Migachev S. A. et al. Low-temperature electrical conductivity of congruent lithium niobate crystals. Physics of the Solid state. 1998. Vol. 40, No. 7. pp. 1190–1192.
11. Rahn J., Hüger E., Dörrer L., Ruprecht B., Heitjans P., Schmidt H. Li self-diffusion in lithium niobate single crystals at low temperatures. Physical Chemistry Chemical Physics. 2012. Vol. 14. pp. 2427–2433.
12. Fielitz P., Borchardt G., Ganschow S., Bertram R., Jackson R., Fritze H., Becker K. Tantalum and niobium diffusion in single crystalline lithium niobate. Solid State Ionics. 2014. Vol. 259. pp. 14–20.
13. Shi J., Fritze H., Weidenfelder A., Swanson C., Fielitz P., Borchardt G., Becker K. Optical absorption of electronic defects and chemical diffusion in vapor transport equilibrated lithium niobate at high temperatures. Solid State Ionics. 2014. Vol. 262. pp. 904–907.
14. Weidenfelder A., Fritze H., Fielitz P., Borchardt G., Shi J., Becker K., Ganschow S. Transport and Electromechanical Properties of Stoichiometric Lithium Niobate at High Temperatures. Zeitschrift für Physikalische Chemie. 2012. Vol. 226. pp. 421–428.