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ABSTRACT: X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic
symmetry Fmm2 (a = 7.914 Å, b = 7.913 Å, and c = 7.937 Å).
Bulletin of the Russian Academy of Sciences Physics 05/2012; 74(8):1112-1114.
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ABSTRACT: The lattice parameters of epitaxial barium strontium titanate films with various thicknesses (from 6 to 960 nm) were measured
as a function of temperature in the normal and tangential directions with respect to the film plane using x-ray diffraction.
The films were grown through the layer-by-layer mechanism by rf cathode sputtering under elevated oxygen pressure. A critical
film thickness (∼ 50 nm) was found to exist, below and above which the films are subjected to compressive and tensile stresses,
respectively. As the temperature varies from 780 to 100 K, the films undergo two diffuse structural phase transitions of the
second order over the entire thickness range. The transitions in the films under tensile stresses are likely to be transformations
from the paraelectric tetragonal to aa phase and then to r phase, whereas the transitions under compressive stresses are transformations from the tetragonal paraelectric to ferroelectric
c phase and then, with further decreasing temperature, to r phase.
PACS numbers77.80.-e–64.70.Nd–77.55.+f
Physics of the Solid State 04/2012; 50(3):485-489. · 0.71 Impact Factor
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ABSTRACT: A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. The ferroelectric nature of the film is proven by in-plane remanent polarization measurement. The highest possible symmetry of the film is determined to be orthorhombic, within the Fm2m space group. Such a structure is rotated by 45° with respect to the substrate and is consistent with tilts of oxygen octahedra doubling the unit cell. This polar structure presents a rather unusual strain-accommodation mechanism.
Journal of Physics Condensed Matter 08/2011; 23(33):332201. · 2.55 Impact Factor
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ABSTRACT: We report a room-temperature high-pressure x-ray and Raman scattering investigation of lead titanate (PbTiO3) up to 63 GPa. Three continuous phase transitions at 13, 20, and 45 GPa between tetragonal-like phases occur. As a result, no evidence is found for a pressure-induced morphotropic phase boundary. Our study provides experimental evidence that PbTiO3 presents a complex sequence of phases accommodating pressure through mechanisms involving oxygen octahedra tilting and reentrance of ferroelectricity.
Physical Review Letters 01/2009; 101(23):237601. · 7.37 Impact Factor
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ABSTRACT: First-order, rhombohedral to orthorhombic, stress-induced phase transitions have been evidenced by bulk charge-stress measurements and X-ray diffraction derived lattice strain measurements in [001]c-poled PZN-4.5PT. The transitions are induced by uniaxial, compressive loads applied either along or perpendicular to the poling direction. In each case, they occur via rotation of the polar vector in the Cm monoclinic plane and the induced lattice strain is hysteretic yet reversible. Although no depoling is observed in the transverse mode, net depolarization is observed under longitudinal stress which is important for the use of [001]c-poled PZN-PT and PMN-PT single crystals in Tonpilz-type underwater projectors.
04/2007;
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ABSTRACT: A first-principles-derived scheme that incorporates ferroelectric and antiferrodistortive degrees of freedom is developed to study finite-temperature properties of Pb(Zr1-xTix)O3 solid solution near its morphotropic phase boundary. The use of this numerical technique (i) resolves controversies about the monoclinic ground state for some Ti compositions, (ii) leads to the discovery of an overlooked phase, and (iii) yields three multiphase points that are each associated with four phases. Additional neutron diffraction measurements strongly support some of these predictions.
Physical Review Letters 11/2006; 97(15):157601. · 7.37 Impact Factor
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ABSTRACT: We report a high-pressure investigation of the relaxor ferroelectric lead zinc niobate PbZn1∕3Nb2∕3O3 (PZN) up to 46 GPa, which is the highest pressure yet attained in the study of relaxors. The evolution of both Raman and x-ray scattering with pressure gives evidence for important pressure instabilities, which find its expression in three successive phase transitions. The observed pressure-induced suppression of diffuse scattering above 5 GPa is similar to recent reports and supports the hypothesis that this is a general feature in relaxors at high pressures.
Phys. Rev. B. 03/2006; 73(9).
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ABSTRACT: The restored strain energy in PbZn1∕3Nb2∕3O3 (PZN) and 9%PbTiO3-doped PZN (PZN-9%PT) relaxor crystals has been studied by means of acoustic emission (AE). Two types of AE activity signals have been recorded: (i) related to temperature- or electric-field-induced macroscopic phase transitions and (ii) associated with formation/disappearance of intrinsic polar nanoregions. Monitoring of AE under varying [001] electric fields has allowed a unique in situ observation of a low-field (1 kV∕cm) irreversible orthorhombic-to-MC phase transition within the morphotropic phase boundary region of PZN-9%PT.
Phys. Rev. B. 01/2006; 73(1).
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ABSTRACT: Ab initio simulations and experimental techniques are combined to reveal that, unlike what was commonly accepted for more than 30 years, perovskites and related materials enhance their ferroelectricity as hydrostatic pressure increases above a critical value. This unexpected high-pressure ferroelectricity is different in nature from conventional ferroelectricity because it is driven by an original electronic effect rather by long-range interactions.
Physical Review Letters 12/2005; 95(19):196804. · 7.37 Impact Factor
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ABSTRACT: Combining density-functional calculations and x-ray diffraction experiments, we show that BiFeO3 epitaxially grown under compressive strain on cubic substrates evolves from the monoclinic Cc phase resulting from the strain-induced deformation of the ground-state rhombohedral R3c phase to the monoclinic Cm phase with increasing misfit, the transition being at about −4.5%/−5.5%. Moreover, the polarization of the Cc phase only rotates instead of increasing for misfit strain ranging from 0% to −4%, due to a strong coupling between polar displacements and oxygen octahedra tilts. This strong interaction is of interest for multiferroics where usually both structural degrees of freedom coexist.
Physical Review B.
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ABSTRACT: A nonlinear thermodynamic theory is applied to strained ferroelectric superlattices and used to determine the dependence of superlattice permittivity on composition. To that end, spontaneous polarizations and field-induced polarization changes in the ferroelectric layers A and B with thicknesses t(A) and t(B) are calculated as a function of the volume fraction phi(A)=t(A)/(t(A)+ t(B)). The existence of a dielectric anomaly at a specific composition phi(A)* is predicted for the superlattices, where only one of ferroelectric layers has nonzero out-of-plane polarization in the uncoupled state. The theoretical predictions agree with the composition dependence of permittivity displayed by the Pb(Sc1/2Nb1/2)O-3/PbTiO3 superlattices grown on SrRuO3-covered SrTiO3
Physical Review B.
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ABSTRACT: A nonlinear thermodynamic theory is applied to strained ferroelectric superlattices and used to determine the dependence of superlattice permittivity on composition. To that end, spontaneous polarizations and field-induced polarization changes in the ferroelectric layers A and B with thicknesses tA and tB are calculated as a function of the volume fraction ϕA=tA/(tA+tB). The existence of a dielectric anomaly at a specific composition ϕA∗ is predicted for the superlattices, where only one of ferroelectric layers has nonzero out-of-plane polarization in the uncoupled state. The theoretical predictions agree with the composition dependence of permittivity displayed by the Pb(Sc1/2Nb1/2)O3/PbTiO3 superlattices grown on SrRuO3-covered SrTiO3.
Phys. Rev. B. 81(14).
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