Dielectric Spectroscopy of the (K0.44Na0.52Li0.04)0.97La0.01Nb0.9Ta0.1O3 Ceramic Obtained by Sol-Gel

(K0.44Na0.52Li0.04)0.97La0.01Nb0.9Ta0.1O3 lead free ceramics were synthesized by sol-gel method. Their morphology, crystal structure and spectroscopic dielectric properties were analyzed by the appropriate techniques. The co-existence of an orthorhombic and a tetragonal ferroelectric phase at room temperature is confirmed by Rietveld analysis. La and Li cations are effective in shifting down the ferroelectric transition temperatures. The tetragonal to cubic transition, (TT-C), takes place at 371 °C while the orthorhombic to tetragonal, (TO-T), occurs at 110 °C, and the maximum relative permittivity (ɛmax) at TT-C is 3000, which is among the highest for KNN-based ceramics obtained by different methods. Conductivity behaves according to Jonscher’s law in the frequency and temperature range of this study. The activation energy values corresponding to the different conduction mechanisms were obtained. The results were compared with those for the same composition obtained by combining the reactive template grain growth (RTGG) technique and the solid-state method.

Dielectric and Piezoelectric Properties of Textured Lead-Free Na0.5Bi0.5TiO3-Based Ceramics

This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na0.5Bi0.5TiO3-0.08K0.5Bi0.5TiO3-0.04BaTiO3 (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method using NaNbO3 (NN) for templates. For textured ceramics with 4 wt% NN templates, a Lotgering factor of 96% and piezoelectric coefficient d33 of 185 pC/N were obtained. Compared to the randomly oriented ceramics, textured ceramics show lower strain hysteresis (H = 7.6%), higher unipolar strain of 0.041% with corresponding large signal piezoelectric coefficient d33* of 200 pm/V at applied field of 2 kV/mm. This enhancement can be explained by the grain orientation along <001> direction by texturing, where an engineered domain configuration is formed after polarization, leading to decreased hysteresis and increased piezoelectric property.