Papers by Keyword: NaNbO₃

Abstract: Lead-free (K_0.5Na_0.5)NbO₃ (KNN) piezoelectric ceramics were studied and synthesized by the seed-induced method. NaNbO₃ crystal was used as seed and prepared by molten salt synthesis (MSS). The average particles size of NaNbO₃ seed crystal was about 1-3 mm. Then, the NaNbO₃ seed was mixed with KNN powder and ball milled for 24 h. The mixed powder was calcined at 700-900 °C and sintered at 1100 °C. The phase structure and morphology of the ceramics were investigated by X-ray diffraction and scanning electron microscope and the electrical properties were studied. The results indicated that all samples showed a pure perovskite phase. The highest density of the ceramic was 93% compared to the theoretical density. The results showed that NaNbO₃seed crystal improved piezoelectric properties of KNN ceramics.

Abstract: Perovskite-based (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ [(1-x) NBT-x NN, x = 0.1, 0.2, 0.3 and 0.4] ceramics were sintered at 1080°C. Dielectric characteristics, crystalline structures, and Raman investigations were carried out on (1-x) (Na_0.5Bi_0.5)TiO₃-x NaNbO₃ ceramics. X-ray diffraction (XRD) patterns showed that NaNbO₃ ceramic would form a solid solution with (Na_0.5Bi_0.5)TiO₃ ceramic, and and unknown or second phases were not observable as well. NaNbO₃ ceramic diffused into the crystalline structure of (Na_0.5Bi_0.5)TiO₃ ceramic and (1-x) NBT_-x NN ceramics still revealed a rhombohedral structure. The temperature-dielectric constant curves showed that as NN content increased, the temperature to reveal the maximum dielectric constant (T_m) was raised, the depolarization temperature (T_d) was shifted to lower value, and the dielectric constant at Tm and the loss tangent at T_d gradually decreased. The Raman bands at 770 and 830 cm^-1 were attributed to the existence of the oxygen vacancies. In this study, the relaxor-type ferroelectric properties of NBT ceramic had been improved as NN ceramic was added.

Abstract: (Na1-xBax)(Nb1-xTix)O3 (NNBTx; x=0.0-0.21) solid-solution ceramics were synthesized and their crystal structure, dielectric properties and piezoelectric properties were investigated. The crystal structure at room temperature of NNBTx varied from orthorhombic to tetragonal with increasing BaTiO3 content x. The phase boundary between orthorhombic and tetragonal at room temperature was confirmed BT content between x=0.08 and 0.09. For x>0.05, it was found that the Curie temperature was decreased with increasing x. The highest electromechanical coupling factor, kp, and the largest piezoelectric constant, d33, were obtained at x=0.09-0.10.

Abstract: The electrical properties and phase transition behavior of the sodium niobate-based solid solution (1-x)Li0.12Na0.88NbO3-xNa0.91Ba0.09Nb0.91Ti0.09O3 [(1-x)LNN12-xNNBT9] ceramics were investigated. The lattice constant changes became discontinuitous between LNNBT0.5 and LNNBT0.7. Moreover, the peak dielectric constant of LNNBT0.7 is twice that of LNNBT0.5. X-ray diffraction analysis and dielectric study confirmed that the different crystal phases of what are LNN-type rhombohedral (x=0), LNN-type orthorhombic (x=0.1, 0.3 and 0.5), NNBT-type orthorhombic (x= 0.7 and 0.9) and NNBT-type tetragonal (x= 1.0) phases. An electromechanical coupling factor of 0.244 was obtained for LNNBT0.7 whose composition is near the boundary between the LNN-type and NNBT-type orthorhombic phases.

Abstract: Piezoelectric and dielectric properties of (LixNa1-x)NbO3 (LNN100x; x≤0.14) ceramics were investigated according to phase transition The highest electromechanical coupling factor, kp, of 0.247 was obtained for LNN12 which has a composition with a morphotropic phase boundary at room temperature. On the other hand, the coupling factor of k33 with longitudinal mode was almost constant for all compositions of x. The dielectric constant, ε r, before poling treatment exhibited a thermal hysteresis near the Curie temperature, TC, for all compositions. The depolarization temperature of LNN6 was higher than the TC before poling treatment. In addition, the peak of free permittivity, ε33 T, was shifted to higher temperature. It was considered that the phase transition was induced by the electric field during poling treatment.