We report the structural, optical, ferroelectric, and dielectric properties of reduced BaTiO₃ samples. For this purpose, oxygen vacancies in BaTiO₃ are created by heating these samples with a Ti metal in a vacuum environment at different temperatures. It is observed that with an increase in oxygen deficiencies, the c/a ratio decreases as compared to that of the oxygen treated sample. The ferroelectric properties of the oxygen deficient samples are visibly different as compared to those of the oxygen treated sample. The disappearance of the P-E loop and the anomaly in the temperature variation of the dielectric constant have been observed; however, the structural phase transition corresponding to ferroelectric phase transitions still persists. Thus, it appears that the anomaly in dielectric data and the presence of the P-E loop are getting masked possibly by the Maxwell-Wagner effect. The presence of Ti⁺³ states in the prepared samples has been confirmed by X-ray absorption near edge structure measurements. The Kubelka-Munk optical absorption shows the presence of extra states below fundamental transition, indicating the emergence of new electronic states within the bandgap, which might be due to Ti⁺³ states. These new states appear at different energy positions, and with different intensities for different samples, which are reduced in the presence of Ti. These new states within the bandgap appear to modify the electronic structure, thereby reducing the overall bandgap, and hence, they seem to modify the ferroelectric and dielectric properties of the samples. Our results may be treated as experimental evidence for theoretically proposed defect states in oxygen deficient or reduced BaTiO₃.

The origin of ferroelectricity in the cubic phase of BaTi _{1− x} Hf _x O ₃ has been investigated. The presence of well-defined ferroelectric polarization versus electric field (PE) hysteresis loop in the samples with global cubic symmetry suggests the presence of ‘local polar regions’, induced possibly due to the huge difference in the electronegativity and also difference in the ionic radii of Hf ⁺⁴ and Ti ⁺⁴ ions, which may lead to local structural disorder. The presence of polar regions is also supported through the appearance of A ₁ (TO) polar mode in Raman spectra which in principle should be absent in the samples with cubic symmetry. The results are discussed in terms of disorder-induced local dipoles due to the electronegativity difference between Hf and Ti ions.

Here, we report the possible origin of natural and magnetic field induced polar order near room temperature (RT) in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_3$. The temperature-dependent Raman spectroscopy (RS) and synchrotron x-ray diffraction experiments disregard any change in the structure at low temperatures, which is not compatible with the emergence of natural ferroelectricity in this sample. Further, inelastic neutron scattering, neutron Compton scattering, neutron resonance transmission analysis and magnetic field-dependent RS experiments, suggest an increase in the delocalization of ${\mathrm{Pr}}^{3+}$ ions in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_3$ with respect to the parent compound $\mathrm{PrFe}{\mathrm{O}}_3$. The evaluation of the present results reveals that more delocalized ${\mathrm{Pr}}^{3+}$ ions and strong spin-phonon coupling in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_3$ seem to be a driving force for the observed natural and magnetic field induced switchable polar order in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_3$. The present results provide a significant contribution in understanding the ferroelectric polarization and progress in the search for RT magnetodielectric materials.

Detailed structural analysis of rare-earth orthoferrites RFeO₃ (R = La, Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, and Yb) has been reported. Polycrystalline samples of RFeO₃ were prepared using the sol-gel method. Structural phase purity of the prepared samples has been investigated using synchrotron X-ray diffraction (SXRD) technique and structural distortion has been estimated using the refinement of SXRD data in terms of Fe–O–Fe bond angles, Fe–O bond lengths, and FeO₆ octahedra distortions. It is observed that with the increase in the ionic radii of R site cation, the lattice constants, R–O bond length, and Fe–O–Fe bond angles increase; whereas Fe–O bond length almost remains constant. The FeO₆ octahedra tilt angles ϕ along (001) direction and θ along (110) direction decrease with increasing ionic radius of R site cations. The structural distortion-parameters of RFeO₃ samples obtained from refinement and compared with the results extracted from modern Bond Valance Sum model (SPuDS) and with density functional theory using WIEN2k package and found consistent with experimental results. The possible correlation between the structural and other physical properties such as transition temperature obtain from differential scanning calorimetry (DSC) has been investigated.