(Pb1-xBix)(Ti1-xMnx)O3: Competing mechanism of Tetragonal-Cubic phase on A/B site modifications

Structural, vibrational and dielectric properties of (Pb1-xBix)(Ti1-xMnx)O3 (PBTM) (0 x 0.50) polycrystalline ceramics have been examined as a function of temperature. Synchrotron-based powder x-ray diffraction was employed to confirm phase purity and crystal structure of samples. Tetragonality (c/a ratio) of the PBTM system exhibit an increase 1.065, 1.066 for x = 0.06 and 0.09 compositions respectively, compare to 1.064 for x = 0 sample. Curie point was found ~763 K and 773 K for x = 0.06 and 0.09 samples respectively. Though, tetragonality start to decreasing from samples with x 0.18, Curie point of the samples started decreasing for x 0.12. Temperature-dependent x-ray diffraction reveals the structural change from tetragonal to cubic structure. Unit cell volume was found to decrease with increasing temperature; indicate these materials are negative thermal expansion type until phase transition temperature, with negative thermal coefficients are -1.571*10-5 /K, -2.44*10-5 /K, and -5.025*10-6 /K for x = 0, 0.06, and 0.09 samples respectively. Raman spectra showed softening of the transverse optical phonon modes and increase in the full width at half maxima with the increase in composition. Field-emission scanning electron microscope equipped with energy dispersive x-ray spectrometer (EDS) confirmed compositional homogeneity and dense type microstructure.
Comment: 26 pages, 12 figures