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Lead-free piezoelectric compounds (0.94)(Na0.5Bi0.5)TiO3–(0.06) BaTiO3 [NBBT (94/06)] + x wt.% Nb5+ (x = 0%, 1%, 1.5%, 2%, and 2.5%) were synthesized by the solid-state reaction route and these powders were pelletized and sintered for dielectric and piezoelectric characterization. The phase coexistence Monoclinic (Cc) + Rhombohedral (R3c) was affirmed using X-ray Powder diffraction analysis. The structural properties like cell parameters and space group of the synthesized ceramics were investigated by the Rietveld refinement analysis. The surface morphology and grain size of the fractured ceramics were explored using SEM imaging technique. The dielectric properties for all the ratios of NBBT (94/06) ceramics were examined using LCR meter. The piezoelectric coefficients such as d33 and g33 of Nb-doped NBBT (94/06) ceramics were investigated. The saturation polarization (Ps) and remanent polarization (Pr) were exhibited from the P–E hysteresis loop analysis at room temperature. The appropriate addition of Nb5+ (x = 1.5%) in NBBT (94/06) material demonstrates eminent dielectric constant and piezoelectric coefficient d33 than other wt.% of Nb. The replacement of Ti4+ with higher radius cations Nb5+ in B-site of ABO3 composes tilting of polar BO6 octahedra resulting in rhombohedra distortion (RD) (90° − α), in addition, the polarizability of ions and various valance states of B-site cations could be responsible for RD (90° − α) ensuing relatively high dielectric constant and piezoelectricity.

Urgent requirement exists to develop the lead-free piezoelectric energy storage devices, sensors and actuators for the reduction of toxicity in the environment. This paper deals with the lead-free ferroelectric single crystals with excellent piezoelectric behaviour. A series of pure and doped (Mn and Nb) (1−x)Na0.5Bi0.5TiO3–xBaTiO3 (NBBT) bulk size single crystals was successfully grown by the top-seeded solution growth (TSSG) method. The crystal growth, phase confirmation, compositional analysis, electric properties and energy storage density were investigated. The NBBT crystal belongs to perovskite structure and is confirmed using X-ray Powder diffraction pattern (PXRD). The elemental composition of the NBBT crystals grown by TSSG was investigated by the Inductively coupled plasma-Atomic Emission spectroscopy (ICP-AES). The electrical properties like dielectric constant (er = 674, 700, 837, 694, 2872 and 378) and dielectric loss (tanδ = 0.2, 0.6, 0.5, 0.7, 0.47 and 0.27) were measured and it was found to be relaxor-type behaviour due to diffuseness of NBBT crystals by the dielectric permittivity. The piezoelectric coefficients (d33 = 374, 290, 167, 110, 410 and 103) and piezoelectric voltage coefficients (g33 = 6.26, 4.6, 2.2, 1.79, 1.6 and 3.0) were obtained. Greater value of remnant polarization (Pr = 87, 46, 30, 0.30, 117 and 0.11), maximum polarization (Pm = 104, 55, 49, 1.08, 136 and 0.34) and lower value of coercive electric field (Ec = 16.5, 13.8, 26, 0.64, 20 and 233) were obtained from the P–E hysteresis loop of NBBT crystals studied to identify good performance of the compositions. The NBBT 90/10 crystal was found to be of 94/06 composition as obtained from ICP-AES. Moreover, NBBT 90/10 was doped by Mn and Nb and its electrical properties were measured. The Mn-doped NBBT 90/10 crystal attained a large energy storage density (W) of 0.27 Jcm−3 at ~ 20 kV cm−1 compared to the undoped and Nb-doped NBBT 90/10 crystal.

A ternary chalcogenide AgBiSe2 (ABS) crystal was grown using the Bridgman–Stockbarger technique followed by XRD and Raman shift analysis to verify the structural properties of the ABS crystal. The temperature (300–4.2 K)-dependent resistivity (ρ) shows semiconductor behavior down to 109 K and transforms to metallic behavior down to 19 K. Due to the localization behavior, the resistance shows an upturn up on further decrease in temperature. Charge defects caused by atomic vacancies as well as anti-site defects are thermodynamically induced, and have the potential to shift the Fermi energy level. The two transitions at 109 and 19 K in ρ(T) demonstrate consequent changes as a semiconductor-to-metal transition. The magnetoresistance MR graph exhibits resistive behavior with respect to the magnetic field applied and displays a ‘U’ shape at 300 K, which changes to a ‘V’ shape at 4.2 K. The Hall effect measurements reveal that the majority carrier is a hole. The carrier density as well as mobility changes with respect to temperature are analyzed within the preview of the Ioffe–Regel criterion. ABS is a promising p-type candidate with efficient characteristics that needs further elaboration for thermoelectric, photonic and photovoltaic applications.

The ternary chalcogenide based pristine AgBiSe2 semiconductor single crystal was studied for the temperature dependence dielectric measurement. The anomalous behaviour of dielectric constant and dielectric loss at higher frequency were discussed in detail. The activation energy due to the dc conductivity as well as hopping frequency were extracted from the Arrhenius equation. Moreover, the charge transport of Ag+ ions as well as the flip-flop between the pairs of Bi4+ and Bi3+ ions is responsible for various electrical properties in this crystal.

The solid solution of 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 NBBT94/06 is a promising material to replace Lead (Pb) based piezoelectric materials. The bulk NBBT 94/06 single crystal was successfully grown by the top-seeded solution growth (TSSG) method. Lead-free piezoelectric NBBT single crystals with a composition across the morphotropic phase boundary (MPB) have been grown by the TSSG method. NBBT 94/06 single crystal, encompassing the rhombohedral to largely monoclinic phase covering the MPB region was grown by the TSSG method. The crystal structure and its electrical properties were investigated. The Laue diffraction pattern confirms that the grown crystal is a single crystal. Rietveld refinement studies disclose the existence of a phase boundary between Monoclinic (Cc) and Rhombohedral (R3c) phases near the MPB. The depolarization temperature (Td), piezoelectric coefficient (d33) and ferroelectric properties were enhanced at MPB.