Structural and dielectric properties of Sr${}^{2+}$ ions substituted NdCrO${}_3$ orthochromate perovskite

In the present work, Nd${}_{(1-x)}$Sr${}_{\left(x\right)}$CrO${}_3$ (x = 0-0.20) compounds were synthesized by doping Sr${}^{2+}$ in NdCrO${}_3$ using the co-precipitation method. We have studied the structural and dielectric properties of these compounds. X-ray diffraction analysis confirms a single phase of pristine NdCrO${}_3$ and Sr${}^{2+}$ doped NdCrO${}_3$ up to 20% concentration having orthorhombic Pnma space group crystal structure. This indicates that Sr${}^{2+}$ has dissolved to a large extent in all doped NdCrO${}_3$ with no impurity phases suggesting Nd${}^{3+}$ has been well substituted by Sr${}^{2+}$. All Sr${}^{2+}$ substituted NdCrO${}_3$ indicates orthorhombic crystal structure (Pnma space group) having mono-phase at room temperature, and the Rietveld refinement also supports it. The obtained Rietveld refined data was studied in detail to know the effect of Sr${}^{2+}$ substitution on bond length and angle. It was observed that as Sr${}^{2+}$ substitution increases, lattice parameters and cell volume also increase. Raman spectra of the prepared material also support the crystal structure. They show that as Sr${}^{2+}$ substitution increases, the intensity of Raman modes decreases and slightly shifts to a lower wave number. In addition, FTIR spectra show the characteristic bands that follow the formation of prepared samples. The dielectric constant (εʹ) and dielectric loss (tanδ) of all samples decrease with the increase of applied electric field frequency, which is explained by Maxwell-Wagner's space charge polarization and hopping mechanism between Cr${}^{3+}$ and Cr${}^{4+}$. The AC conductivity of all samples increases with frequency and follows Jonscher's power law, which confirms the charge hopping and localized motion. The imaginary part of the electric modulus shows the relaxation peak that shifts towards the higher frequency value, which means relaxation time decreases as the Sr${}^{2+}$ substitution increases. The influence of grain and grain boundaries are studied by complex impedance analysis where a single semi-circle is observed in the cole-cole plot. The resistance due to grain and grain boundaries decreases as the Sr${}^{2+}$ substitution increases.