## Abstract

Solid solutions of (1-x)Pb(Sc_{2/3}W_{1/3})O _{3}-(x)PbTiO_{3} and (1-x)Pb(Sc_{2/3}W _{1/3})O_{3}-(x)PbZrO_{3} (PSW-PT and PSW-PZ) show remarkably different dielectric responses. Even though PT has a much higher Curie temperature (490 °C) than PZ (230 °C), addition of Ti up to x≈0.25 decreases T_{ε,max} - in contrast to the increase of T_{ε.max} for the substitution of PZ. Concentrations of Ti with x>0.25 lead to a strong increase in T_{ε,max}. The structural origins of this behavior were studied by x-ray and neutron diffraction, pair distribution function (PDF) analysis and density functional theory (DFT) calculations. For x<0.25 the B cations form a 1:1 ordered doubled perovskite structure (space group Fm3̄m) in agreement with the "random site model," where the ordered structure consists of one B sublattice occupied by Sc and the other by a random mixture of the remaining cations. The B site order is reduced by incorporation of Zr, but highly stabilized by Ti with the degree of order in excess of 95% for x≤0.25. The results of PDF analysis and DFT calculations show that locally the atoms are significantly displaced from their average lattice positions and that T_{ε,max} is strongly correlated with the cation displacements. The initial anomalous decrease of T_{ε,max} in PSW-PT is due to the suppression of ferroelectricity by a decrease in the perovskite volume and is related to reduced Pb displacements. For xlt;0.25 the contribution to ferroelectric polarization from Ti and W are restricted because of the high B-site ordering. However, as the order is reduced for x>0.25, the active Ti and W cations couple their displacements and dominate the dielectric response, driving T _{ε,max} up. For PZ substitution, the lack of ordering leads to nearly linear growth of T_{ε,max} corresponding to a uniform increase in Pb and B-cation displacements.

Original language | English |
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Article number | 214101 |

Pages (from-to) | 214101-1-214101-13 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 69 |

Issue number | 21 |

DOIs | |

State | Published - Jun 2004 |

Externally published | Yes |

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