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Lead-free ferroelectric materials are essential for environment-friendly solid-state cooling technology. In this respect, the electrocaloric effect of lead-free Ba0.8−xSr0.2SmxTiO3 (x = 0.01–0.05) ceramics has been investigated. The Rietveld refinement reveals that all the ceramics exhibit tetragonal symmetry and the tetragonality decreases for x > 0.03, which is the major reason behind the decrease in both isothermal entropy change and adiabatic temperature change. The degree of diffuseness parameter is enhanced by doping of Sm3+, which confirms the formation of polar nanoregion and the enhancement of the electrocaloric effect parameter by adding extra entropy. The relaxor behavior of the prepared samples is also confirmed by estimating the degree of deviation parameter (Δ T m = 77 K ) from the 1 ε r vs. T curve. So, the temperature stability of the prepared ceramics is improved in a broad temperature window. The highest isothermal entropy change (Δ S) , adiabatic temperature change (Δ T) , and electrocaloric strength ( Δ T Δ E ) are found to be 1.230 Jkg−1 K−1, 0.862 K, and 0.028 73 K cm/kV at 316 K, respectively, for Ba0.77Sr0.2Sm0.03TiO3. [ABSTRACT FROM AUTHOR]

Polycrystalline [(0.5) Bi0.5Na0.5TiO3-(0.5) LaFeO3] multiferroic composite is prepared by using the solid-state reaction method. The crystal structure of both phases is characterized by using the X-ray diffraction method (XRD) and confirms the presence of rhombohedral (i.e., bismuth sodium titanate) and orthorhombic (i.e., lanthanum ferrite) phases in the composite. The microstructure of the composite is analyzed using field emission scanning electron microscopy (FESEM). The crystal structure is further studied with Raman spectroscopy. The present composite exhibits ferroelectric and ferrimagnetic-like properties, revealing its multiferroic behavior. Furthermore, the impedance analysis of the composite shows the negative temperature coefficient of resistance behavior. The present study describes the structural and physical properties of the possible lead-free multiferroic composite. [ABSTRACT FROM AUTHOR]

Temperature-dependent dynamic ferroelectric hysteresis of semiconductor–relaxor ferroelectric (0–3) type composite {0.30(ZnO)–0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBTO)]} has been investigated using polarization–electric field (P–E) loops, current density–electric field (J–E) curves, and temperature-dependent dielectric permittivity. It is well known that the polarization reversal mechanism can be explained by the concept of ferroelectric domain switching kinetics, which depends strongly on the temperature. The present work ascribes the role of polar nanoregion induced thermal depolarization field on the temperature-dependent ferroelectric hysteresis loop along with polarization reversal mechanism. The present composite exhibits unique ferroelectric switching behavior above the thermal depolarization temperature (∼100 °C), which is observed in P–E and J–E loops. The depolarization field-induced pinched P–E loops of a BNBTO solid solution above Td (∼100 °C) have been significantly overcome by the incorporation of semiconductor (ZnO) particles, which extensively described the underlying mechanism in the present context. In addition, the temperature-dependent polarization reversal mechanism displays unique two-stage processes [low-T (<100 °C) and high-T (>100 °C)] for the minor loops (∼30 and 40 kV) and saturated loops (∼45 kV) as described by the electric field–temperature phase diagram. The present results may provide a distinct way to Bi0.5Na0.5TiO3-based solid solutions for high-temperature piezoelectric applications. [ABSTRACT FROM AUTHOR]

Currently, semiconductor–relaxor ferroelectric (0–3) type composites are promising lead-free ferroelectric candidates for high-temperature piezoelectric applications. Among all, 0.30(ZnO)-0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3] is one of the most studied composites by researchers. Therefore, to understand the role of ZnO on the polarization reversal process and domain states of (Bi0.5Na0.5)0.94Ba0.06TiO3, the dynamic ferroelectric hysteresis of the present composite has been investigated as a function of electric field amplitude (E0) and frequency (f). According to the power law, a set of scaling relations between the loop area ⟨A⟩ with E0 and f have been established for minor and saturated loops, which take the form of ⟨ A ⟩ ∝ f − 0.389 E 0 4.586 and ⟨ A ⟩ ∝ f − 0.021 E 0 1.066 , respectively. Also, it is interesting to note that the frequency-dependent ferroelectric hysteresis loops [for the saturated field (E0) = 50 kV/cm] exhibit the unique two-stage scaling behavior. Additionally, the origin of enhancement in the domain switching process for minor loop regions has been correlated with the presence of a semiconductor (ZnO), which is extensively discussed in the present study. [ABSTRACT FROM AUTHOR]

Multiferroic composites are the current research interest due to their multi-functional behavior with promising electrical and magnetic properties compared to single crystallographic phase multiferroic materials. Hence, multiferroic composites of (1−x)Bi0.85La0.15FeO3-(x)NiFe2O4 (x = 0 to 0.50) have been investigated by considering Bi0.85La0.15FeO3 as a ferroelectric phase and NiFe2O4 as a magnetic phase. The crystal structure was examined by analyzing the X-ray diffraction (XRD) patterns. Different crystal structure parameters were obtained from the Rietveld refinement of XRD patterns. An increase in the lattice parameters of both Bi0.85La0.15FeO3 (BLFO) and NiFe2O4 (NFO) phases has been observed with the increase in the percentage of NiFe2O4 in the composites. Absorption peaks in Raman spectra shift toward lower frequencies with the increase in the percentage of NFO in the composite. Variation of lattice parameters and shifting of the Raman modes suggest the lattice strain at the interfaces of BLFO and NFO. Theoretical magnetizations were calculated for all composites by using the sum rule (using the magnetization of individual phases) and compared with experimentally observed magnetization. Interestingly, the experimental values of magnetizations of the composites are more than the theoretically calculated ones. It could be due to the lattice strain, which was observed from the XRD and Raman analysis. [ABSTRACT FROM AUTHOR]

The high temperature electrical phase transitions of (1 − x) Bi0.5Na0.5TiO3–(x) Bi0.5K0.5TiO3 (x = 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35) relaxor ferroelectrics have been investigated by employing the dielectric spectroscopy technique. The Rietveld refinement of the XRD patterns reveals the increase of the lattice distortion (c/a) from 1.001 to 1.006 in the tetragonal crystal symmetry (P4mm) with the increase of the BKT (x = 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35) mole fraction. The different bonds vibration (Bi3+/Na+/K+–O and Ti4+–O) related to phonon modes have been studied by analyzing the Raman spectra. The relaxor antiferroelectric ordering temperature (Td: depolarization temperature) of Bi0.5Na0.5TiO3 (BNT) reduce from ~ 200 to ~ 91 °C with the increase of the BKT mole fraction. This observation is well correlated to the formation of polar nanoregions (PNRs) due to the compositional fluctuation in the local crystal structure. Also, Td varies with the frequency of the applied electric. It suggests the presence of the PNRs and, subsequently exhibits the relaxor ferroelectric behavior. The activation energy to activate the PNRs reduces from 2.573 to 2.383 meV with the increase of the BKT mole fraction in the solid solutions. Reduction in remanent electrical polarization and the electrical coercive field in temperature dependent ferroelectric hysteresis loops suggest the relaxor antiferroelectric behavior of the solid solutions (x ≥ 0.15) near the depolarization temperature. [ABSTRACT FROM AUTHOR]

Ferroelectric materials with crystal symmetry transition from single phase to multiphase coexistence exhibit anomalous photosensitive properties. The optical properties (optical band gap and photosensitive) found on non-centrosymmetric and centrosymmetric systems achieved research interest because of their interesting behavior. In this regard, the lead-free polycrystalline Ba 1- x Sr x TiO 3 (BSTO, 0⩽x⩽0.3) has been synthesized to explore its crystal structure, dielectric, light absorption, and photocurrent sensing properties for various applications. Both experimental and theoretical studies on BSTO (0⩽x⩽0.3) ceramics confirm the crystal symmetry transition with the reduction of band gap as compared to pristine BaTiO 3 . This crystal symmetry transition plays an important role in varying the various physical properties as it involves the transition from the polar phase to the non-polar phase. The optical band gap has been estimated experimentally by the Tauc plot method and found that there is a small variation of energy band gap from 3.615 eV to 3.212 eV with Sr substitution. The highest dielectric constant was found to be 5327 at lower frequency on Ba 0.76 Sr 0.24 TiO 3 after that for further increase in Sr concentration the dielectric constant decreases because of the introduction of the non-polar phase. A strong correlation between crystal structure and physical properties (dielectric, optical, etc.) has been observed. The photocurrent of the samples is significant which reveals that the sample is influenced by the photons. In a nutshell, the present study deepens the understanding of the correlation between crystal structure and various physical properties of BSTO and, hence provides an idea of required design parameters to construct a ferroelectric system for better photosensitive nature suitable for device applications., (© 2023 IOP Publishing Ltd.)

The effect of A-site nonstoichiometric in La 3+ modified Bi 0.5 (Na 0.80 K 0.20 ) 0.5 TiO 3 /BNKT solid solution on crystal structure and electrical properties have been investigated. Evolution of crystal structure from rhombohedral (R3c) to tetragonal (P4bm) symmetry with reduction of the lattice distortion has been observed. The Raman spectra analysis is well supported to the crystal structure study from the XRD patterns analysis. The presence of charge defects due to non-stoichiometric composition and the reduction of oxygen vacancies have been confirmed by the x-ray photoelectron spectra (XPS) of the respective elements. The FESEM (field emission scanning electron microscopy) micrographs clearly show the reduction of grain size with the incorporation of La 3+ in A-site of BNKT. The multiple dielectric anomalies near depolarization temperature (T d ) and temperature at maximum dielectric value (T m ) in the temperature dependent dielectric curves ascribe the diffuse phase transition with relaxor ferroelectric nature. The dielectric anomalies at T d and T m become more pronounce with the increase in addition of La 3+ into BNKT lattice. The presence of charge defects with A-sites complexity leads to interrupt the long range polar ferroelectric domains and, forms the polar nanoregions (PNRs). The competition between ferroelectric R3c symmetry and non-polar P4bm symmetry with the addition of La 3+ into the BNKT lattice induces an intermediate modulated phase, which exhibits the antiferroelectric in nature having pinched ferroelectric hysteresis loop.