Magnetic, dielectric and calorimetric studies on 0.9BiFeO 3 -0.1BaTiO 3 indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic Tc due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous evidence for magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO 3 based system.
We have carried out a detailed Rietveld analysis of x-ray powder diffraction data of Pb(ZrxTi1−x)O3 (PZT) compositions across the morphotropic phase boundary (MPB) region (x=0.515, 0.520, 0.525, 0.530). It is shown that the structure of PZT is pure tetragonal for x⩽0.515 with space group P4mm. In the MPB region, 0.515<x<0.530, the tetragonal and monoclinic (space group: Cm) phases are found to coexist as a result of a first order phase transition between the low temperature monoclinic and high temperature tetragonal phases. Further, arguments are advanced to show that the hitherto believed rhombohedral structure (FRHT) of PZT for 0.530⩽x⩽0.62 is more likely to be monoclinic.
Structural and dielectric evidences are advanced to show that the Sr1-xCaxTiO3 (SCT) system undergoes an antiferroelectric (AFE) phase transition in the composition range 0.18=x=0.40. Stabilization of the AFE phase, instead of the ferroelectric (FE) phase known for 0
The morphotropic phase boundary in the phase diagram of the technologically important Pb(Zr x Ti 1Àx )O 3 (PZT) ceramics has been traditionally believed to separate ferroelectric tetragonal and rhombohedral phase regions. This old picture has come under close scrutiny during the last eight years following the discovery of new monoclinic phases in the Cm and Cc space groups. This article presents a brief overview of these discoveries in which the use of multiple diffraction probes (X-ray, electron, neutron diffraction) in conjunction with physical property measurements has played a crucial role. A new phase diagram of PZT showing the stability fields of these structures below room temperature is also presented.
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.
The structure of
(1-x)[Pb(Mg1/3Nb2/3)O3]-xPbTiO3 is
tetragonal and rhombohedral for x⩾0.35 and x⩽0.30,
respectively. The intrinsic width of the morphotropic phase
boundary region (0.30
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