Anomalous behavior of dielectric response of quantum paraelectric CaTiO$_3$ with iron impurities

Herein we report on the studies of lattice dynamics and crystal structure of natural perovskite with the general formula CaTiO$_3$:0.01Fe by dielectric spectroscopy and $X$-ray diffraction in a wide temperature range. In contrast to the “chemically pure” synthetic perovskite, the lattice dynamics of the Fe-containing natural sample exhibits a structural instability in the vicinity of 240 K. Our studies of the behavior of magnetic moment of CaTiO$_3$:0.01Fe demonstrate that in the temperature region from 4.3 to 300 K this material is paramagnetic. No changes in the crystal symmetry have been observed in the structural studies, which can be explained by the small degree of lattice distortions, as has been observed previously for isotopically substituted SrTiO$_3^{18}$. Conductivity measurements and analysis of the dielectric response dispersion of CaTiO$_3$:0.01Fe have shown that the dispersion is due to the Maxwell–Wagner mechanism and can be attributed to oxygen vacancies present in the mineral.