Growth and study of single crystals of the (Na,Li)Nbo3 solid solutions

Plateletlike transparent (Na,Li)NbO₃ (NLN) single crystals with up to 7 mol % LiNbO₃ possessing a perovskite structure are synthesized by the method of spontaneous crystallization from NaBO₂ flux. Based on the X-ray diffraction data and dielectric measurements of these single crystals, the phase x-T diagram of these solid solutions is constructed in the vicinity of the NaNbO₃ composition. It differs from the x-T diagrams established for the Na_{1 ? x} Li_xNbO₃ ceramic.     

Domain structure of Na1 − x LixNbO3 crystals

The domain structure of single-crystal and ceramic samples of Na_{1 ? x} Li_xNbO₃ solid solutions (at x ≤ 0.14) in the orthorhombic ferroelectric and antiferroelectric phases at room temperature is investigated by optical and electron microscopies and X-ray diffraction. The characteristic feature of the domain structure is the formation of 90° complexes consisting of laminar domains with a specific orientation relative to the lattice of the initial cubic phase. Consideration is given to the specific features in packing of these complexes and typical configurations of domains in the crystals. Observations revealed that the domain structure can involve 90°, 60°, 120°, and 180° boundaries, as well as (hhl) boundaries of the S type whose orientation depends on the cell distortion and changes with a variation in _x. The indices of these boundaries are determined. The density of 180° boundaries in the ferroelectric phase is very low compared to that of non-90° boundaries.     

Acoustic emission and thermal expansion of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> and Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> crystals

The temperature dependence of the elongation per unit length for Pb(Mg_1/3Nb_2/3)O₃ crystals unannealed after growth and mechanical treatment is investigated in the course of thermocycling. It is revealed that this dependence deviates from linear behavior at temperatures below 350°C. The observed deviation is characteristic of relaxors, is very small in the first cycle, increases with increasing number n of thermocycles, and reaches saturation at n≥3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350°C. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n>3. For (1?x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ crystals, the dependence of the temperature of this acoustic emission maximum on x exhibits a minimum. It is assumed that the phenomena observed are associated with the phase strain hardening due to local phase transitions occurring in compositionally ordered and polar nanoregions.