Phase precipitation in the Bi1−xCaxMnO3 compounds (x = 0.4–0.6)

Abstract

Charge ordering (CO) in Bi1−xCaxMnO3 (x = 0.4–0.6) has been investigated by temperature-dependent high-resolution neutron powder diffraction (NPD), X-ray powder diffraction (XRD) and physical property measurements. Anomalies in magnetization, resistivity and lattice parameters have been observed around the CO transition temperature (TCO) reported in the literature. However, a scrutiny of the NPD and XRD data at different temperatures and the electron diffraction experiments at 300 K give no evidence of a long-range CO below the reported TCO. Instead, NPD and XRD reveal a coexistence of two orthorhombic phases in the samples below the reported TCO. All the experiments suggest that one of the coexisting phases is originated from a precipitation or an incomplete structural transition of the other phase and the reported TCO corresponds to the precipitation reaction or structural transition temperature, rather than a CO transition temperature.