Abstract
The room temperature crystal structure and phase evolution of Ca-substituted Na1/2Bi1/2TiO3(NBCT) at A-site were investigated systematically using X-ray diffraction (XRD) combined with Raman spectroscopy. While XRD patterns of calcined powders exhibited the expected rhombohedral (R3c) phase at room temperature due to low Ca concentration, the corresponding sintered samples displayed peak splitting for all Bragg peaks, appearing as shoulders for all studied compositions. This departure from the average rhombohedral (R3c) to a non-rhombohedral structure is an indication of a new phase evolution of this system. The optimal Rietveld refinement corresponds to the coexistence of two phases, rhombohedral and tetragonal (R3c+P4bm) in the equilibrium state at room temperature. The proposed model describes the growth of a stable high-temperature tetragonal (P4bm) phase within the rhombohedral (R3c) matrix at room temperature. This work is the first XRD macroscale detection of a stable tetragonal (P4bm) phase in rhombohedral complex perovskite at room temperature.
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