Influence of hydrostatic pressure on electrical relaxation in non-homogeneous bismuth manganite - Lead titanate ceramics

The composite 0.96 BM–0.04 PT ceramics was sintered from non-polar bismuth manganite (BM) and ferroelectric lead titanate (PT) components. We show influence of small amount of PT on structure ordering of BM. The X-ray pattern analysis showed occurrence of three phases: orthorhombic Pbam related to BiMn2O5, cubic Pn3¯m attributed to δ−Bi2O3, and tetragonal P4¯21c related to unrecognized phase Bi20TiO32 isostructural to β−Bi2O3. Occurrence of these three phases reflected in variation in chemical compositions detected using transmission electron microscopy. Correspondence between nano-structural features of BM-PT and electrical relaxation processes was studied. The DC resistivity temperature dependence exhibited crossover from variable range hopping to nearest-neighbor hopping of small polarons. Furthermore, three electrical relaxations attributed to small polaron hopping were distinguished. Two relaxations corresponded to BM-originated phases. One relaxation exhibited crossover from variable range hopping to nearest-neighbor hopping of small polarons. Second relaxation showed crossover from variable range hopping to Vogel-Fulcher temperature dependence. Third relaxation, related to nearest-neighbor hopping of small polarons, was attributed to Bi20TiO32:Pb phase derived from PT compound. Structural disorder of BM-PT phases reflected in Fermi glass features manifested by variable range hopping of polarons. Moreover, we showed sensitivity of BM-PT ceramics on high hydrostatic pressure. Applied hydrostatic pressure, p = 800 and 1600 MPa, shortened the relaxation times. We propose equation of state for relaxation process related with PT amount doped to BM ceramics. Equation of state of dielectric includes response to varied hydrostatic pressure and temperature, that is to different thermodynamic conditions. Correspondence between effects of applied hydrostatic pressure and presumed chemical pressure was considered as consequence of inter-diffusion of Pb, Bi, Mn, and Ti ions and their mutual substitution. •Occurrence of unrecognized phase Bi20TiO32 was confirmed using XRD and TEM.•Inter-diffusion of ions provided tensile and compressive stresses.•Applied external hydrostatic pressure shortened relaxation time.•Hydrostatic pressure dominated defects-related chemical pressure.•Electric permittivity included conductivity and relaxation processes.