Ferroelectric-paraelectric phase transition in PbHf_0.2Ti_0.8O₃studied by neutron powder diffraction

Abstract

Neutron powder diffraction data, collected over the temperature range 10-810 K, have been analysed in order to study the ferroelectric-paraelectric transition in the ferroelectric compound PbHf0.2Ti0.8O3. This transition appears at 670 K between the low-temperature tetragonal phase and the high-temperature cubic phase. From high-resolution neutron powder diffraction data (3T2-LLB), the tetragonal structure of the ferroelectric phase has been refined at 10, 300 and 400 K using a Rietveld-type method: space group P4mm, Z = 1; at T = 10 K, at = 3.9299(4) Å, ct = 4.1239(5) Å and Vt = 63.689 Å3; at T = 300 K, at = 3.9405(4) Å, ct = 4.1038(5) Å and Vt = 63.723 Å3; and at T = 400 K, at = 3.9468(4) Å, ct = 4.0901(5) Å and Vt = 63.713 Å3. In addition, a neutron powder thermodiffractometry experiment (D1B-ILL) has been performed to study in situ the temperature induced phase transition. From sequential Rietveld refinements, the thermal dependence of the cationic displacements has been analysed and a spontaneous polarization has been derived. From a generalized effective field theory, the first-order character of the phase transition has been established. Finally, the structural results obtained on the ferroelectric PbHf0.2Ti0.8O3 are discussed in reference to PbTiO3 and PbHf0.4TiO0.6O3 compounds.

In situ neutron diffraction studies of single crystals and powders during microwave irradiation

“…This phase was included in all refinements. Similar effects have been seen before in BaTiO 3 [34][35][36] and related materials 37,38 and attributed to small particles stabilized in the cubic phase through local strain. All the structural parameters of this additional phase were refined independently of the majority phase, and optimised parameters are displayed in Table 3; the cell parameter of this phase is given with that of the majority phase in Fig.…”

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

“…It is enhanced NTE for 0.7PT-0.3BiFeO 3 (a V = À2.5 Â 10 À5 K À1 , 298-773 K), but much reduced NTE for 0.7PT-0.3Bi(Zn 1/2 Ti 1/2 )O 3 (a V = À6.0 Â 10 À6 K À1 , 298-773 K). 87 The trend in Fig. The c/a ratio exhibits the same trend as the unit cell volume as a function of temperature.…”

“…It is interesting to note that the unit cell volume of PbTi 0.8 Hf 0.2 O 3 shows a similar decreasing slope as a function of temperature to its P S , which also indicates that the probable coupling role in NTE and P S . 87 The trend in Fig. 19b can guide the design and control of NTE for PT-based ferroelectrics.…”

Investigation of Ternary System PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 with Morphotropic Phase Boundary Compositions

“…using impedance spectroscopy and differential scanning calorimetry, and the complete PHT phase diagram was reported . In addition, the ferroelectric‐to‐paraelectric phase transitions in PbHf 0.2 Ti 0.8 O 3 and PbHf 0.4 Ti 0.6 O 3 were found to be on the order of 670 and 620 K, respectively, by using neutron powder diffraction . To date, however, limited research has been carried out to investigate the PHT‐based ternary systems, which are expected to exhibit similar behavior to PZT‐based ternary systems with high dielectric and piezoelectric properties near MPB regions …”