9 research outputs found

    Quasivertical line in the phase diagram of single crystals of Pb Mg1 3 Nb2 3 O3 -x PbTiO3 (x=0.00, 0.06, 0.13, and 0.24) with a giant piezoelectric effect

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    We show that the phase diagram of the (001) Pb Mg1 3 Nb2 3 O3 -x PbTiO3 (PMN- x PT) (x=0.00, 0.06, 0.13, and 0.24) and (111) PMN-0.24PT lead-magnesium niobate mixed with lead titanate possesses a quasivertical line in the E electric field - T temperature plot, which hardly depends on the field. The existence of this line has been confirmed by independent studies of single crystals grown in different laboratories, by measuring the dielectric permittivity, compliances, and optical transmission, also in different laboratories. A thermal hysteresis inherent to first order phase transitions complicates the phase diagram. The piezoelectric coefficients of the (001) PMN- x PT (x = 0.06 and 0.13) have two peaks versus temperature, at finite fields. The first peak is due to the quasivertical phase boundary. The second is in the vicinity of a turning point of the Tm (E) temperature of the dielectric permittivity diffuse maximum. We show that the second peak prevails at reasonable fields, and the piezoelectric coefficients have comparatively large values at this peak, even at small x. © 2007 The American Physical Society

    A Theory of Ferroelectric Phase Transition in SrTiO3_3 induced by Isotope Replacement

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    A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in SrTiO3_3 is developed. The proposed model gives consistent explanation between apparently contradictory experimental results on macroscopic dielectric measurements versus microscopic lattice dynamical measurements by neutron scattering studies. The essential feature is described by a 3-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of TiO6_6 cluster. The effect of isotope replacement is taken into account through the tunneling frequency between the excited states. The dielectric properties are analyzed by the mean field approximation (MFA), which gives qualitative agreements with experimental results throughout full range of the isotope concentration.The phase diagram in the temperature-tunneling frequencycoordinate is studied by a QMC method to confirm the qualitative validity of the MFA analysis.Comment: 26 pages, 8 figure

    The Energetics of Li Off-Centering in K1‚ąíx_{1-x}Lix_xTaO3_3; First Principles Calculations

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    K1‚ąíx_{1-x}Lix_{x}TaO3_3 (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercells were used to investigate these phenomena. Lattice dynamics calculations for KLT exhibit a Li off-centering instability. The energetics of Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li pairs can be considered "seeds" for polar nanoclusters in KLT. Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and interactions with neighboring Li-ions all enhance the polarization from Li off-centering. Calculated hopping barriers for isolated Li-ions and for nearest neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental dielectric data.Comment: 14 pages including 10 figures. To Physical Review B. Replaced after corrections due to referees' remark

    Percolation with constraints in the highly polarizable oxide KTaO 3:Li

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    PACS. 71.55.Jv Disordered structures; amorphous and glassy solids - 78.20.Bh Theory, models, and numerical simulation - 42.65.Ky Harmonic generation, frequency conversion,

    Low-temperature phase transformations in weakly doped quantum paraelectrics: novel features and quantum reentrant dipolar glass state in KTa0.982Nb0.018O

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    An unusual sequence of phase transitions (PT) and reentrant dipole glass-like phase formation at low temperatures was found recently in KTaO3 weakly doped with Li and Nb (K0.9986Li0.0014Ta0.976Nb0.024O3) [Phys. Rev. B 63 (2001) 172]. We report on detailed low frequency (100 Hz-1 MHz) permittivity and Raman light scattering studies of similar composition, but without Li admixture, KTa1-xNbxO3 with x = 0.018 (KTN1.8). The aim of the study is to answer the question if the reentrant dipole glass-like phase exists in KTN1.8 and what is the microscopic origin of this phase. A detailed study of the sharp low-temperature PT observed at T-C similar to 27 K revealed properties inherent to the reentrant glass-type state at lower temperatures. The substitution of Nb for Ta influences the TOI soft lattice mode and leads to PT with the long-range ferroelectric ordering. A crossover to an order-disorder polar microregion dynamics with a non-standard epsilon'(T) behaviour and dipole glass-like formation were found below T-C (at similar to 15 K), which is attributed to the randomness of the Nb distribution. A crossover to the Iona-range order was found under a dc bias field. (C) 2004 Elsevier Ltd. All rights reserved