Lead-free ceramic materials produced from bismuth sodium titanate (Na_0.5Bi_0.5TiO₃, NBT)-bismuth potassium titanate (K_0.5Bi_0.5TiO₃, 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 (ε_r') 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.

Solid solutions (1-x-y)(Na_0.5Bi_0.5)TiO₃-xBaTiO₃-y(K_0.5 Bi_0.5)TiO₃ with (x (mol.%) = 0, 7 and 100); y(mol.%) = 0, 20 and 100) compositions have been prepared by a conventional solid-state reaction method, and their structure, dielectric properties and depolarization temperature have been examined. At room temperature, X-ray diffraction (XRD) patterns reveal that the crystalline structure of the ceramics was perovskite. The morphotropic phase boundary (MPB) of the ternary system lying between rhombohedral (R3c) and tetragonal (P4mm) phases is in the range of (x (mol.%) = 7 and y (mol.%) = 20). The Raman-active modes for 0.73NBT-0.07BT-0.20KBT were separated and identified under the framework of group theory. SEM micrographs illustrate the quasi-uniform distribution of the grains, which are compact. The dielectric properties of the ceramics were studied in the frequency range of 1 kHz–100 kHz from ambient temperature to 600 °C. Dielectric measurements indicate that all ceramics show a diffuse phase transition near the temperature (T_m) for diffusivity of the order of 1.4–1.7 and a shift of (T_m) towards high temperatures. The resistance and capacitance of the various contributors (grain and grain boundary) in our samples are also discussed using a brick-layer model. Excellent piezoelectric properties for d₃₃ = 146 pCN⁻¹ and electromechanical coupling factors k_p = 29.4% were observed at morphotropic phase boundary (MPB), which was assumed to be associated with the coexistence of rhombohedral and tetragonal phases and accurate grain size. This work establishes a new approach for improving lead-free piezoelectric ceramics based on 0.73NBT-0.07BT-0.20KBT.

(1-x)(Na₀.₅Bi₀.₅)TiO₃-xCaTiO₃ Lead-free piezoelectric systems, positioned near the morphotropic phase boundary, were synthesized for varying compositions (x = 0.0, 0.05, 0.10, 0.15, and 0.20) using the solid-state reaction route. This study delves into the comprehensive investigation of the compositional effects on phase, structure, and electrical characteristics. Specifically, a morphotropic phase boundary (MPB) involving rhombohedral (R3c) and orthorhombic (Pnma) structures was seen in a (1-x)NBT-xCT crystal structure close to the composition of x = 0.10. Information on the pure phase formation and grain size of the intended composite system has been obtained using Rietveld refinement of the X-ray diffraction (XRD) diagram as well as scanning electron microscopy (SEM). The impact of the CT phase on the NBT lattice was investigated through an analysis of the charge density distribution. Using Williamson-Hall plots from XRD data, the average particle diameter was estimated to be between 131.87 nm and 136.54 nm. The relative permittivity increases with the addition of Ca²⁺, according to dielectric measurements. All ceramics exhibit a diffuse phase transition near (Tm) with a diffusivity range of 1.5–1.8, and a downward shift in depolarization temperature (Td). At the morphotropic phase boundary (MPB), excellent dielectric properties were observed at x = 0.10, which are attributed to the presence of both rhombohedral and orthorhombic structures as well as an appropriate particle size. The conduction process at different temperatures is thermally activated, as determined by the frequency-dependent ac conductivity.

Barium strontium lead titanate ((Ba_0.85Sr_0.15)_1-x Pb _x TiO₃), along with various compositions (x(mol %) = 0, 2, 4, and 8), was synthesized through the conventional sol-gel reaction method. Following this, the resultant powders underwent a carefully controlled calcination process at 1000 °C for a period of 4 h. The examination of the crystalline phase of the calcined ceramics was conducted at room temperature using X-ray diffraction. Rietveld refinement of the XRD data, performed using FullProf, revealed that the samples exhibited a tetragonal structure within the space group P4mm. The impact of Pb doping on the lattice structure of BaSr_1-x TiO₃ was explored by analyzing the charge density distribution. The FTIR analysis unveiled a distinct absorptive band within the 450-600 cm^-1 range, indicative of the stretching and bending vibrations associated with TiO₆ octahedra. Notably, sintering the material at 1150 °C for 4 h resulted in improved densification, as observed in scanning electron microscopy images showcasing a nearly uniform distribution of densely packed grains. Through the utilization of Williamson-Hall plots derived from XRD data, the average particle diameter was estimated to fall within the range of 131.87-141 nm, with an associated uncertainty ranging from 5 to 10%. Additionally, the dielectric characteristics unveiled the presence of a negative dielectric constant (ε_r) spanning the frequency range from 1 kHz to 2 MHz. The (Ba_0.85Sr_0.15)_1-x Pb _x TiO₃ ceramic displayed a widespread occurrence of negative permittivity, emphasizing the influence of dielectric resonance. The investigation revealed that the sintered ceramic with the formula (Ba_0.85Sr_0.15)_1-x Pb _x TiO₃ exhibited exceptional piezoelectric properties, achieving the highest piezoelectric constant (d₃₃ = 137 pC/N) and electromechanical coupling factor (k _p = 0.49).