Detailed structural and dielectric properties of Lanthanum-doped barium titanate [Formula: see text]Lax[Formula: see text]O3 ceramic powders BLTx (where [Formula: see text]; 0.10; 0.20; 0.30 and 0.40)/BT, BLT10, BLT20, BLT30 and BLT40, synthesized by the sol gel process, calcined at 900∘C for 3[Formula: see text]h and sintered at 1250∘C for 6[Formula: see text]h, have been investigated. The phase formation and crystal structure of the samples were checked by X-ray diffraction (XRD) and Raman spectroscopy. The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La; results that have been confirmed by Rietveld Refinement technique. The estimated average crystallite size of the samples was about 23[Formula: see text]nm. Dielectric parameters (dielectric permittivity and losses) were determined in the temperature range room temperature (RT) — 280∘C and in the frequency range 500[Formula: see text]Hz–2[Formula: see text]MHz. La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature, and the frequency dependence of the permittivity shows that the samples with [Formula: see text] and [Formula: see text] reach their resonance frequency. The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1[Formula: see text]kHz to 2[Formula: see text]MHz at various temperatures to confirm the contributions from grains and grain-boundaries. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters; it was found that the grain boundaries resistance is dominant at room temperature. The frequency dependence of the parameters permittivity, losses and AC conductivity reveals that the relaxation process is of the Maxwell–Wagner type of interfacial polarization.

Lead-free ceramic materials produced from bismuth sodium titanate (Na0.5Bi0.5TiO3, NBT)–bismuth potassium titanate (K0.5Bi0.5TiO3, KBT) have been developed through a solid-state reaction technique. The structural, dielectric, and piezoelectric characteristics of the ceramic materials were analyzed. Based on the XRD investigation, the morphotropic phase boundary (MPB) was determined for the composition (x (%) = 16 and 20). The effects of the KBT phase on the NBT lattice were examined using the charge density distribution. Furthermore, the dielectric properties indicated the presence of a negative dielectric constant (εr′) as a function of frequency between 1 kHz and 2 MHz. Negative permittivity was observed globally in the (1 – x)­NBT–xKBT ceramic which reflects the effect of the dielectric resonance. The grain conduction effect is revealed through the complex impedance spectrum in the form of a semicircular arc within the Nyquist plot. In addition, the samples studied revealed a non-Debye relaxation phenomenon. The relaxation time was determined based on the Vogel-Fulcher law for all samples. DC conductivity was carried out on the ceramics material and revealed that the resistance decreases with increasing temperature indicating a negative temperature coefficient of resistance. The AC conductivity as a function of frequency for different temperatures suggests the presence of a thermally activated conduction mechanism. The activation energy has been determined based on the Arrhenius plot of the DC electrical conductivity as well as the relaxation frequency.

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Abstract. In this work, we prepared series of Ba 1-x Sr x TiO 3 (BS x T) powders, with different strontium concentrations (x = 0, 0.025, 0.75, 0.10, 0.125 and 0.15), by the sol-gel method. The variation of structure in the Ba1-xSrxTiO3 system was analyzed using XRD and Raman techniques. The field dependence of dielectric relaxation and conductivity was measured over a wide frequency range from room temperature to 400 °C. The activation energy, calculated from the thermal variation of the conductivity for different frequencies, showed that the Sr has significant effects on the properties of BaTiO 3 . Relaxation times extracted using the imaginary part of the complex impedance (Z''(ω)) and the modulus (M''(ω)) were also found to follow the Arrhenius law and showed an anomaly around the phase transition temperature.

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