Papers by Author: Ghulam Shabbir

Abstract: BiScO₃-xPbTiO₃ (BS-PT) of perovskite type structure (with x~0.64) were prepared by solid state ceramic process with addition of calcium fluoride (CaF₂) in different molar ratios (0.5, 1.0 and 4.0 mol%). The doped compositions were found to have different symmetry compared with parent material. The 0.5 mol% doped sample was found to possess enhanced rhombohedral phase as compared to other compositions while he Curie temperature (T_c) was not affected appreciably. Small dielectric peaks were observed, indicating phase transition, at temperature lower than T_c in all the samples except 4.0% doped composition. At room temperature doping reduced the loss factor. d₃₃ and P_r reduced rapidly with doping. The characteristics of BS-PT ferroelectric ceramics became harder with the addition of CaF₂.

Abstract: The capacitance of (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) [001]-oriented single crystal was examined as a function of temperature and applied external dc electric field. The phase transition temperatures under the applied electric field were measured upon cooling the crystal (zero-field heating field-cooling condition) from paraelectric cubic phase. From these data, temperature versus electric field phase diagram of PMN-xPT crystal have been constructed and discussed.

Abstract: The aging characteristics and influence of electric field poling on the phase transitions in (1-x)Pb (Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) [110]-oriented single crystal were examined through temperature dependent complex capacitance study. In addition to two phase transition anomalies exhibited by the crystal in the virgin state, other phase transition instabilities were observed in the complex capacitance of the crystal under the external applied electric field. The aging behavior deviated from the linear logarithmic law and followed the stretched exponential expression typical for relaxor ferroelectrics. Moreover, aging decreased with frequency while it became faster with increase in temperature towards the paraelectric – ferroelectric structural phase transition temperature.

Abstract: Micro-Brillouin light scattering experiments were performed on flux grown D-type (monoclinic, P2₁/c) Ho₂Si₂O₇ single crystal from room temperature to 850 K. Both the hypersonic velocity (V_LA) and related elastic constant (c₃₃) of the longitudinal acoustic phonons propagating along 001-direction showed a small dispersion at T565 K whereas the same could not be observed clearly in attenuation/damping. The overall temperature dependent behavior of elastic constant and hypersonic velocity was attributed to the lattice anharmonicity of the crystal in the investigated temperature range.

Abstract: The electrical properties of [001]-oriented morphotropic phase boundary (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-33%PT) single crystal have investigated as a function of temperature and frequency. The ac-conductivity exhibited continuous dispersion at all temperatures and frequency range examined and was associated to the thermally activated space charge carriers and local off-centering of Ti4+ and Pb2+ ions. The variations in ferroelectric phase transition temperatures observed in the poled state were associated to the polarization fluctuations and phase co-existence.

Abstract: High-resolution Brillouin scattering technique was applied to study the dynamics of central peaks (CPs) in two relaxor ferroelectric systems, PLZT-x/65/35 ceramics and PMN-33%PT [001] single crystals, respectively. It was found that CPs appear very close to an intermediate temperature, Td, for both type of specimens. The temperature dependence of CPs was attributed to the appearance and subsequent growth of polar nanoregions (PNRs) intrinsic to relaxor materials.

Abstract: Thin films of organic semiconductor based azo-dye, OD 25, of the average thickness, 750 ± 10 nm, were desposited successfully on the glass substrate for gas sensing applications. Electrical conductivity was of the film as measured by impedance spectroscopy, showed an increase with frequency that was attributed to non-metallic nature of the film. Moreover, single conduction mechanism and negligible contact resistance showed good quality of the sensor film. Deposited film with Al and Ag electrodes showed good conductance when exposed to water and ethanol vapors.

Abstract: Dielectric properties and structural morphology of the Sc2O3 free and reduced lead content piezoelectric ceramic system, (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 (BMZ-xPT), were investigated in this study. The average grain size of the fresh fractured surfaces was of the order of ≤1 μm to ∼3 μm. The dielectric constant, loss tangent, Curie temperature, remnant polarization, coercive field, piezoelectric coefficient, and the planer coupling constant of ceramics in the vicinity of the morphotropic phase boundary (MPB) (x∼0.55) were, ∼1450, 0.0952, ∼553 K, 29 (μC/cm2) , 23 (kV/cm), ∼185 pC/N, and ∼30%, respectively. It was observed that with decreasing PbTiO3 contents the phase transition anomaly became broadened. The position of the dielectric constant maximum (ε′max) did not show any significant variation with probe frequency, exhibiting character of diffuse phase transition like many other disordered perovskites.