Neutron scattering study of PbMg $_{\mathsf{1/3}}$Ta $_{\mathsf{2/3}}$O$_{\mathsf 3}$ and BaMg $_{\mathsf{1/3}}$Ta $_{\mathsf{2/3}}$O$_{\mathsf 3}$ complex perovskites

Abstract

Neutron scattering investigations were carried out in PbMg 1/3 Ta 2/3 O3 and BaMg 1/3 Ta 2/3 O3 complex perovskites. The crystal structure of both compounds does not show any phase transition in the temperature range 1.5 -730 K. Whereas the temperature dependence of the lattice parameter of BaMg 1/3 Ta 2/3 O3 follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg 1/3 Ta 2/3 O3 exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. We find that in PbMg 1/3 Ta 2/3 O3, lead ions are displaced from the ideal positions in the perovskite structure at all temperatures. Consequently short-range order is present. This induces strong diffuse scattering with an anisotropic shape in wavevector space. The temperature dependences of the diffuse neutron scattering intensity and of the amplitude of the lead displacements are similar.

Relaxing with relaxors: a review of relaxor ferroelectrics

“…As already discussed in Section 3.8, the Pb ions are displaced in PMT. The magnitude of the Pb displacements is temperature-dependent and reaches a maximum of about 0.34 Å at 20 K [217]. As the displacements of the different atoms are correlated, the temperature-dependent diffuse scattering is observed in PMT single crystals and has a similar temperature dependence to that of the Pb displacements, as shown in Figure 82.…”

“…The average crystal structure of PMT is, at all temperatures, the perovskite structure with the P m3m space group [213,217]. Unlike PMN, however, no modification of the crystalline structure of PMT has been detected when an electric field is applied [213].…”

Negative thermal expansion in functional materials: controllable thermal expansion by chemical modifications

“…74,75,89,91,92 As temperature cools down from T B , the effect of SVFS is produced due to the frozen PNRs. 74,75,89,91,92 As temperature cools down from T B , the effect of SVFS is produced due to the frozen PNRs.…”

“…74,75,89,91,92 As temperature cools down from T B , the effect of SVFS is produced due to the frozen PNRs. 91 In compositions of A(Mg 1/3 Ta 2/3 )O 3 (A = Pb and Ba), Pb is an ion with strong ferroelectric activity while Ba is a weak one. Good examples can be seen in thermal expansion in complex perovskites of A(Mg 1/3 Ta 2/3 )O 3 (A = Pb and Ba) which gives good evidence for such suggestion (Fig.…”

“…Some Mn-based compounds exhibit anomalous thermal expansion by antiferromagnetic spin ordering. 91 Since NTE of R 2 Fe 17 occurs with its magnetic ordering temperature, the NTE temperature range can be controlled by adjusting the magnetic ordering temperature. 200 Thermal expansion in antiferromagnetic Mn-Ge alloys can be chemically controlled by Ge content.…”