Structural phase transitions coupled with prominent dielectric anomalies and dielectric relaxation in [(CH3)(3)NH](2)[KCo(CN)(6)] and mixed [(CH3)(3)NH](2)[KFexCo1-x(CN)(6)] double perovskite hybrids

摘要

The crystals of pure [(CH3)(3)NH](2)[KFe(CN)(6)] (TrMAFe) and [(CH3)(3)NH](2)[KCo(CN)(6)] (TrMACo) as well as their mixed crystals (TrMAFe(x)Co(1-x)), with different ratios of x = 0, 0.12, 0.18, 0.49, 0.56, 0.73, 0.81, 1.0, have been grown from aqueous solutions. The structure of TrMACo has been determined at 360 K to be cubic (Fm3m). In phase II (100 K), the TrMACo crystal is monoclinic (C2/c). The thermal stability of the pure and mixed crystals has been determined by using both DTA and TGA. Based on the DSC results, we have found a single phase transition (PT) for both pure and mixed crystals. The Fe(iii) concentration was estimated by using the SEM technique. We have found a linear relationship between the PT temperature (T-c) and the molar concentration of Fe(iii). Based on the obtained results, a phase diagram has been constructed. The mechanism of the structural PT has been discussed based on the results of dielectric relaxation and H-1 NMR and X-ray spectroscopy measurements. The results confirmed that the PT mechanism of both pure and mixed crystals is related to the change in the dynamic state of the TrMA(+) cations. The dielectric activation energy changes linearly with the mole fraction ranking from 35 to 38 kJ mol(-1), for the mixed crystals.