Pretransitional diffuse neutron scattering in the mixed perovskite relaxorK1−xLix

Abstract

Several previous studies of K 1Ϫx Li x TaO 3 ͑KLT͒ have revealed the presence, above the structural transition, of polar nanoregions. Recently, these have been shown to play an essential role in the relaxor behavior of KLT. In order to characterize these regions, we have performed a neutron-scattering study of KLT crystals with different lithium concentrations, both above and below the critical concentration. This study reveals the existence of diffuse scattering that appears upon formation of these regions. The rodlike distribution of the diffuse scattering along cubic directions indicates that the regions form in the shape of discs in the various cubic planes. From the width of the diffuse scattering we extract values for a correlation length or size of the regions as a function of temperature. Finally, on the basis of the reciprocal lattice points around which the diffuse scattering is most intense, we conclude that the regions have tetragonal symmetry. The large increase in Bragg intensities at the first-order transition suggests that the polar regions freeze to form large structural domains and the transition is triggered by the percolation of strain fields through the crystals.

Second-harmonic generation and x-ray diffraction studies of the pretransitional region and polar phase in relaxorK(1−x)LixTaYokota1, Uesu2, Malibert3 et al. 2007Phys. Rev. B393290View full textAdd to dashboardCite

“…The temperature interval ⌬T of the pretransitional region is determined to be 40 K in both KTL-3 and KTL-7, which agrees with the result of the neutron diffuse scatterings in KLT-6. 7 The possible picture of the pretransitional region is as follows: In the cubic phase, dipole moments produced by off-centered Li ions align along one of the symmetry equivalent ͗100͘ directions. Below T B , individual Li dipoles start to associate to form PNRs as a result of intracorrelations of Li dipoles.…”

“…5 On the other hand, Toulouse et al pointed out that KLT is a kind of relaxor based on dielectric dispersion characteristics 6 and neutron diffuse scattering experiments. 7 Recent observations using an optical second-harmonic generation ͑SHG͒ microscope also support the relaxor nature of KLT-3 because of the marked history dependence of SHG intensities 8 which is similar to that of a prototype relaxor Pb͑Mg 1/3 Nb 2/3 ͒O 3 ͑PMN͒. 9,10 To be a real relaxor, the following criteria should be satisfied: ͑1͒ the characteristic frequency dispersion obeys the Vogel-Fulcher ͑VF͒ law and ͑2͒ polar nanoregions ͑PNRs͒ appear in a temperature range above T m .…”

Diffuse neutron scattering study of a disordered complex perovskitePb(Zn1/3La-Orauttapong1, Toulouse2, Robertson3 et al. 2001Phys. Rev. B782540View full textAdd to dashboardCite

“…This study follows a similar study of another mixed perovskite relaxor, K 1Ϫx Li x TaO 3 ͑KLT͒, which provided the correlation length or size of the polar nanoregions as a function of temperature. 13 In contrast to KLT, PZN exhibits not only substitutional chemical disorder but also charge disorder. Moreover, due to lone electron pair effects, Pb 2ϩ ions form partially covalent bonds with the neighboring oxygen atoms, which results in the off-centering of lead and in an additional local electric dipole moment.…”

Influence of lattice polarizability on interacting Li-induced dipoles distributed in incipient ferroelectricKTaO3

“…[17][18][19][20][21][22] Much attention has also been directed to determining the correlation length of the Li-induced dipoles through various experiments, such as Raman scattering, 23 dielectric measurement, 24 second-harmonic generation, 25,26 x-ray diffuse scattering, 27 and neutron diffuse scattering. 28 The reported correlation lengths are summarized in Table II in the study by Yong et al 28 Azzini et al have also proposed the presence of two kinds of correlation: dipolar and quadrupolar. 25 Raman scattering 29 and x-ray scattering 27 studies have revealed that the structural change takes place in KLT from cubic to tetragonal at the dipole freezing temperature.…”