(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 structures of the samples. Tetragonality (c/a ratio) of the PBTM system increased to 1.066 from 1.064 for the compositions x = 0.12 for pure PbTiO3 sample and decreased with further increase in x (≥0.18). The temperature of phase transition increased to a maximum of 773 K for the sample x = 0.09. The peak corresponding to the ferroelectric-paraelectric phase transition for x = 0.09 sample was accompanied by a change in crystal structure from tetragonal to cubic at ∼773 K, as confirmed by the temperature dependent XRD data. Unit cell volume was found to decrease with increase in temperature, indicating the existence of a negative coefficient of thermal expansion in all samples up to the temperature of phase transitions. The thermal coefficients were found to be −1.571 × 10−5/K, −2.44 × 10−5/K, and −0.50 × 10−5/K for x = 0, 0.06, and 0.09 samples, respectively. Raman spectra showed softening of the transverse optical phonon modes and their full width at half maxima (FWHM) increased 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.