Amarnath Sen

Particle size dependence of magnetization and phase transition near TN in multiferroic BiFeO3

We report results of a comprehensive study of the phase transition at TN (∼643K) as a function of particle size in multiferroic BiFeO3 system. We employed electrical, thermal, and temperature dependent x-ray diffraction studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime of 2–300K under a magnetic field of 100–10000Oe both on bulk and nanocrystalline systems. While in the bulk system a sharp endothermic peak at TN together with a broad feature, ranging over nearly ∼100K (ΔT), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at TN, is found to occur both at TO and TN across ΔT in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metasta...

Temperature Dependent Electrical Properties of PZT Wafer

The electrical and electromechanical properties of lead zirconate titanate (PZT) wafers were investigated and compared with PZT bulk. PZT wafers were prepared by tape casting technique. The transition temperature of both the PZT forms remained the same. The transition from an asymmetric to a symmetric shape was observed for PZT wafers at higher temperature. The piezoelectric coefficient (d33) values obtained were 560xa0pc/N and 234 pc/N, and the electromechanical coupling coefficient (kp) values were 0.68 and 0.49 for bulk and wafer, respectively. The reduction in polarization after fatigue was only ~3% in case of PZT bulk and ~7% for PZT wafer.

Synthesis, Characterization and Vapour Sensing Properties of Nanosized ZnFe2O4

In recent years, there has been a renewed interest on spinel ferrites for their remarkable versatile applications. Among AFe2O4, zinc ferrite (ZnFe2O4) has gained special importance due to its application in gas sensing, drug delivery and magnetic resonance imaging. Nanocrystalline powder of ZnFe2O4 with average size of 25-30 nm was synthesized using citrate-gel method. Thermogravimetric analysis and XRD confirmed the formation of nanocrystalline ZnFe2O4 at 400°C. The band appearing below 700 cm–1 in the FTIR spectrum confirmed the presence of Zn(Fe-O) group. Microstructural investigation was done on SEM and TEM. The response of ZnFe2O4 towards alcohol and acetone vapour at 350°C was studied. The sample showed n-type conductivity with excellent vapour sensitivity.

Effect of Lamination Pressure on the Strain Response of PZT Based Multilayer Actuators

Lamination under pressure at an elevated temperature is one of the steps of fabricating multilayer ceramics including multilayer actuators. It is generally assumed that during the lamination process the pressure applied, albeit within a range, has a trivial role in the ultimate behaviour of fired multilayer actuators. However, in the present work, we show that lamination pressure plays an important role in the most critical property, viz, strain response of multilayer actuators. Depending on the lamination pressure, the strain values may change more than hundred percent, though other properties like hysteresis, capacitance, tan δ and coupling coefficient remain nearly unaffected.

Coexistence of Strong Frequency Dispersion of Dielectric Constant and Temperature-Invariant Curie Peaks in Doped Ferroelectric Ceramics

We report an unusual dielectric behavior of acceptor (copper)-doped barium titanate, where along with sharp temperature-invariant Curie peaks, a frequency dispersion, which is much stronger than that of a normal ferroelectric material has been observed. The value of γ (exponent of modified Curie–Weiss law) has been found to be 1.5 at 1 kHz, which is intermediate to those of a ferroelectric and a relaxor material. However, at 1 MHz frequency, γ is equal to 1 similar to a normal ferroelectric. The simple reasoning of additive coupling of ferroelectricity and Maxwell–Wagner relaxation falls short of explaining these observations. Such behaviour can be understood by considering the role of an impressed local ac field across the grain boundaries of the samples, the field being generated from the alternating space charge polarization at low frequencies.