Fe and W co-substituted BaTiO3 perovskite ceramics, compositional formula BaTi$_{0.5}$(Fe$_{0.33}$W$_{0.17}$)O$_3$, were synthesized by the standard solid-state reaction method and studied by X-ray diffraction, scanning electronmicroscopy and spectroscopy ellipsometry. The prepared sample remains as double phases with the perovskite structure. The structure refinement of BaTi$_0.5$(Fe$_{0.33}$W$_{0.17}$)O$_3$ sample was performed in the cubic double and hexagonal setting of the Fm$\bar{3}$m and P6$_3$/mmc space groups. Spectral dependence of optical parameters; real and imaginaryparts of the dielectric function, refractive index, extinction coefficient and absorption coefficient were carried out in the range between 1.4 and 4.96 eV by using the ellipsometry experiments. Direct bandgap energy of 4.36 eV was found from the analysis of absorption coefficient vs. photon energy. In addition, the oscillator energy, dispersion energy and zero-frequency refractive index values were found from the analysis of the experimental data usingWemple–DiDomenico single-effective-oscillator model.

In this work, we have investigated the magnetic and magnetocaloric properties of Pr$_{0.8−x}$Bi$_x$Sr$_{0.2}$MnO$_3$ ($x = 0$, 0.05 and 0.1) polycrystalline manganites prepared by sol–gel route on the basis of a phenomenological model. Temperature dependence of magnetization indicates that all our samples exhibit a second order paramagnetic to ferromagnetic transition with a decrease in temperature. A correlation between experimental results and theoretical analysis based on a phenomenological model is investigated. The magnetic and magnetocaloric measurements are well simulated by this model. Under a magnetic applied field of 5 T, the theoretical absolute values of the maximum of magnetic entropy change $\Delta S_{\rm Max}$ are found to be equal to 5.33, 3.33 and 2.97 J kg$^{−1} K$^{−1}$ for $x = 0$, 0.05 and 0.1 respectively. The relative cooling power and the specific heat capacity values are also estimated. The predicted results permit us to conclude that our compounds may be promising candidates for magnetic refrigeration at low temperatures.