Phase transitions in semiwet derived (Pb1−xBax)ZrO3 ceramics for the composition range 0⩽x⩽0.30 have been investigated by dielectric measurements at various frequencies during heating and cooling cycles. The paraelectric (PE) to ferroelectric (FE) to antiferroelectric (AFE) sequence of phase transitions is observed for 0⩽x<0.20. On increasing the Ba2+ content from x=0 to x=0.05, the thermal hysteresis associated with the AFE–FE phase transition increases from 11 to 100 °C. This is attributed to the increase in the piezoelectric coupling between the strain and polarization. For x=0.20, the FE phase does not transform into the AFE phase on cooling. Pronounced deviations from the regular FE behavior are observed on increasing the Ba2+ content to x=0.25. For x=0.30, the temperatures corresponding to the peak values of the real and imaginary parts of the dielectric constant become frequency dependent indicating relaxor FE behavior. It is shown that the polar clusters present in the PE phase undergo Vogel–Fulcher type relaxational freezing in the relaxor FE phase. The results of temperature dependent polarization measurements confirm the findings of the dielectric studies. It is proposed that Ba2+ substitution modifies the AFE and FE interactions of the PbZrO3 matrix in such a manner that their strengths become comparable for x=0.30 leading to the glassy or relaxor behavior.

Dielectric and x-ray diffraction evidences are presented to show that the antiferroelectric to ferroelectric phase transition in (Pb0.90Ba0.10)ZrO3 ceramics is not reversible during the cooling cycle. It is shown that the stable antiferroelectric phase recovers from the metastable ferroelectric matrix on aging at room temperature. The kinetics of recovery of the antiferroelectric phase is very sluggish. It is pointed out that this type of irreversibility occurs in field induced antiferroelectric to ferroelectric transitions also. This may have serious implications for the actuator applications of these materials. It is proposed that the large transformation strains associated with the antiferroelectric orthorhombic to ferroelectric rhombohedral phase transition is responsible for this irreversibility.

Activated carbon (AC) was prepared from Lapsi seed stone by chemical activation with Potassium hydroxide at 400°C. The AC was characterized by pH, moisture content, Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), methylene blue (MB) and iodine (I 2 ) number. FT-IR spectra indicated the presence of various oxygen containing functional groups on the surface of AC. SEM images show the highly porous characteristics of AC with full of cavities. The Iodine number of AC revealed that the AC was found to be highly micro-porous. The adsorption of methylene blue by prepared AC was analyzed by the Langmuir and Freundlich adsorption isotherms. The data fitted well to the Langmuir isotherm with monolayer adsorption capacity 158 mg/g. The analysis showed that the AC prepared from Lapsi seed stone activated with potassium hydroxide could be a low-cost adsorbent with favorable surface properties.

We have carried out high temperature x-ray diffraction studies on (Pb1−xBax)ZrO3(PBZ) to correlate the large thermal hysteresis (∼100 °C for x=0.05) and irreversibility (for x=0.10) of the antiferroelectric (AFE)–ferroelectric (FE) phase transition observed in dielectric measurements with structural changes. It is shown that for both the compositions, the sequence of phase transitions during heating is orthorhombic antiferroelectric (AO) to rhombohedral ferroelectric (FR) and then to cubic paraelectric (PC). The wide phase coexistence region (∼80 °C for x=0.05 and ∼160 °C for x=0.10) and the arrest of the FR to AO transition for x=0.10 during cooling strongly indicate first order character of the AO–FR transition. It is shown that the transformation strains associated with the AO to FR transition increases with Ba2+ concentration from a value of 0.6% for x=0 to 0.9% for 0.10. Similarities of the AO–FR transition in PBZ with nonthermoelastic martensitic transformations are pointed out. The FR to PC transition is also shown to be first order but with a small thermal hysteresis (∼10 °C) and a small discontinuous change in the cell volume (∼0.5%).

The relative stability of the ferroelectric rhombohedral (F R ) and antiferroelectric orthorhombic (A O ) phases of (Pb 1Ϫx Ba x )ZrO 3 has been investigated as a function of Ba 2ϩ concentration ͑x͒ using phenomenological theory considerations. It is shown that all the unknown parameters in the free-energy expressions for the F R and A O phases can be evaluated using the dielectric and x-ray-diffraction data as a function of temperature. We show that the differences in the energies of antiferroelectric and ferroelectric phases decrease with increasing Ba 2ϩ concentration, indicating the gradual destabilization of the antiferroelectric phase. The theoretically predicted critical composition xϭ0.17Ϯ0.0025, above which no antiferroelectric phase can exist, is found to be in excellent agreement with the experimental observations.