High Pressure Induced Isostructural Transformation in Ferromagnetic Semiconductor Ca2FeNbO6-δ Double Perovskite

Abstract

In this work, we report a rare earth free double perovskite, Ca2FeNbO6-δ (CFNO), synthesized via a sol–gel assisted autocombustion technique, with an orthorhombic (Pnma) structure at ambient conditions. In situ high pressure synchrotron X-ray diffraction studies reveal a reversible isostructural transition above 8.2 GPa, without altering its orthorhombic structure up to 12.2 GPa. The UV–vis diffuse reflectance spectroscopy shows CFNO to exhibit semiconducting behavior with a band gap of 2.1 eV and a refractive index of 2.6. Temperature dependent magnetization reveals a transition from paramagnetic to ferromagnetic ordering at Tc of 49 K. From the Curie–Weiss analysis, the Curie–Weiss temperature (θcw) and Curie–Weiss constant (C) are found to be 19 K and 2.63 cm3K/mol, respectively, along with an effective magnetic moment of 4.58 μB. The frequency dependent ac susceptibility without dispersion behavior near 49 K rules out the possible presence of spin glass or cluster glass. Isothermal magnetization studies indicate that the reduced magnetization is attributed to antisite disorder, which weakens the magnetic interaction due to randomness of Fe and Nb atoms at the 4b Wyckoff position. Further, a photocatalytic response against methylene blue (MB) dye with degradation efficiency of 92.5% suggests its suitability in dye degradation applications. Moreover, CFNO may be proposed for multifunctional applications in the field of pressure sensors and spintronics.