Grain orientation and anisotropy in the physical properties of SrBi2(Nb1-xVx)(2)O-9 (0 <= x <= 0.3) ceramics

摘要

SrBi2(Nb1-xVx)(2)O-9 (0 less than or equal to x less than or equal to 0.3 in molar ratio) ceramics have been fabricated via conventional sintering at elevated temperatures. Interestingly sintering the pellets in the 1320 - 1470 K temperature range yielded partially grain oriented ceramics. The orientation factor (f) monitored via X-ray powder diffraction studies was found to increase with increasing V2O5 content and reached 83% for x = 0.3. The increment in (f) was not that significant with increase in sintering temperature and its duration. The microstructural studies suggest that V2O5 has a truncating effect on the abnormal platy growth of SBN grains. The dielectric constant (epsilon(r)) and loss (D) measurements as functions of both temperature and V2O5 content have been carried out along the directions parallel (epsilon(rp)) and perpendicular (epsilon(rn)) to the cold pressing axis of the pellet. The anisotropy (epsilon(rn)/epsilon(rp)) associated with epsilon(r) was found to be 1.11 at 300 K and 2.1 at the Curie temperature, (T-c) respectively. Different dielectric mixture formulae that were employed to analyze the effective dielectric constants of these samples with varying porosity confirmed that the experimental value of epsilon(r) was comparable with that obtained using Wiener's formula. Impedance spectroscopy was employed to rationalize the electrical behavior of these ceramics. The pyroelectric coefficients along the directions parallel and perpendicular to the pressing axis of the grain oriented (83%) SBN ceramic at 300 K were 0.13145 mC/m(2)K and 0.26291 mC/m(2)K respectively. The ferroelectric properties of these grain-oriented ceramics were better in the direction perpendicular to the pressing axis than those in the parallel direction. (C) 2003 Kluwer Academic Publishers. [References: 24]