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Neutron powder diffraction data, collected over the temperature range 10–770 K, have been analysed in order to make a detailed characterization of the sequence of phase transitions occurring in the Hf-rich ferroelectric PbHf0.8Ti0.2O3, titanium hafnium lead oxide. Over the whole temperature range this compound undergoes two phase transitions, which involve cationic displacements and octahedral deformations (tilt and/or distortion) leading to strongly distorted perovskite-type structures. The first transition appears around 415 K between two ferroelectric rhombohedral phases: a low-temperature nonzero-tilt phase FRL (space group R3c) and an intermediate zero-tilt phase FRH (space group R3m). The second one, detected around 520 K, is associated with a ferroelectric to-paraelectric transition between the FRH phase and the PC cubic phase (space group Pm3m). From high-resolution neutron powder diffraction data (diffractometer 3T2-LLB, Saclay, France, λ = 1.2251 Å), the crystallographic structure of the three successive phases has been accurately determined at the following temperatures: T = 10 K (FRL): space group R3c, Z = 6, ahex = 5.7827 (1), chex = 14.2702 (4) Å, Vhex = 413.26 (2) Å3; T = 150 K (FRL): space group R3c, Z = 6, ahex = 5.7871 (1), chex = 14.2735 (4) Å, Vhex = 413.98 (3) Å3; T = 290 K (FRL): space group R3c, Z = 6, ahex = 5.7943 (1), chex = 14.2742 (5) Å, Vhex = 415.04 (3) Å3; T = 440 K (FRH): space group R3c, Z = 6, ahex = 5.8025 (1), chex = 14.2648 (4) Å, Vhex = 415.94 (3) Å3; T = 520 K (PC): space group Pm3m, Z = 1, acub = 4.1072 (2) Å, Vcub = 69.29 (1) Å3. In addition, a neutron powder thermodiffractometry experiment, performed between 290 and 770 K (diffractometer D1B-ILL, Grenoble, France, λ = 2.533 Å), has been used to study in situ the temperature-induced phase transitions. From sequential Rietveld refinements, the temperature dependence of the cation displacements and the rotation and/or distortion of oxygen octahedra was derived.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768199011453/sh0134sup1.cif
Contains datablocks global, 1, 2, 3, 4, 5

txt

Text file https://doi.org/10.1107/S0108768199011453/sh01341sup2.txt
Supplementary material

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Text file https://doi.org/10.1107/S0108768199011453/sh01342sup3.txt
Supplementary material

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Text file https://doi.org/10.1107/S0108768199011453/sh01343sup4.txt
Supplementary material

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Text file https://doi.org/10.1107/S0108768199011453/sh01344sup5.txt
Supplementary material

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Text file https://doi.org/10.1107/S0108768199011453/sh01345sup6.txt
Supplementary material

Computing details top

For all compounds, cell refinement: Fullprof; program(s) used to refine structure: Fullprof; molecular graphics: CaRIne, version 3.0.

(1) lead hafnate titanate top
Crystal data top
Hf0.8O3PbTi0.2γ = 120°
Mr = 407.52V = 413.26 (2) Å3
Rhombohedral, R3cZ = 6
a = 5.7827 (1) ÅNeutron radiation, λ = 1.2251 Å
c = 14.2702 (4) ÅT = 10 K
α = 90°
Data collection top
Diffractometer in Debye-Scherrer geometryk =
h = l =
Refinement top
S = 2.0239 parameters
158 reflectionsWeighting scheme based on measured s.u.'s w = 1/(σ2), σ2 = y
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb000.2835 (1)0.0073 (3)
Hf000.0126 (1)0.0004 (4)*0.80
Ti000.0126 (1)0.0004 (4)*0.20
O0.1427 (2)0.3461 (2)0.08330.0085 (3)*
Bond lengths (Å) top
Hf—O2.01O—O2.92
Hf—O2.12Pb—O2.49
Ti—O2.01Pb—O2.76
Ti—O2.12Pb—O3.10
O—O2.80Pb—O3.35
O—O3.02
(2) lead hafnate titanate top
Crystal data top
Hf0.8O3PbTi0.2γ = 120°
Mr = 407.52V = 413.98 (3) Å3
Rhombohedral, R3cZ = 6
a = 5.7871 (1) ÅNeutron radiation, λ = 1.2251 Å
c = 14.2735 (4) ÅT = 150 K
α = 90°
Data collection top
Diffractometer in Debye-Scherrer geometryk =
h = l =
Refinement top
S = 2.0039 parameters
158 reflectionsWeighting scheme based on measured s.u.'s w = 1/(σ2), σ2 = y
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb000.2821 (1)0.0127 (3)
Hf000.0121 (1)0.0008 (2)*0.80
Ti000.0121 (1)0.0008 (2)*0.20
O0.1458 (2)0.3456 (2)0.08330.0105 (3)*
Bond lengths (Å) top
Hf—O2.01O—O2.91
Hf—O2.11Pb—O2.51
Ti—O2.01Pb—O2.78
Ti—O2.11Pb—O3.08
O—O2.80Pb—O3.33
O—O3.01
(3) lead hafnate titanate top
Crystal data top
Hf0.8O3PbTi0.2γ = 120°
Mr = 407.52V = 415.04 (3) Å3
Rhombohedral, R3cZ = 6
a = 5.7943 (1) ÅNeutron radiation, λ = 1.2251 Å
c = 14.2742 (5) ÅT = 290 K
α = 90°
Data collection top
Diffractometer in Debye-Scherrer geometryk =
h = l =
Refinement top
S = 2.2839 parameters
158 reflectionsWeighting scheme based on measured s.u.'s w = 1/(σ2), σ2 = y
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb000.2793 (1)0.0243 (4)
Hf000.0114 (2)0.0023 (2)*0.80
Ti000.0114 (2)0.0023 (2)*0.20
O0.1525 (2)0.3448 (3)0.08330.0162 (3)*
Bond lengths (Å) top
Hf—O2.02O—O2.91
Hf—O2.11Pb—O2.54
Ti—O2.02Pb—O2.81
Ti—O2.11Pb—O3.04
O—O2.80Pb—O3.29
O—O3.00
(4) lead hafnate titanate top
Crystal data top
Hf0.8O3PbTi0.2γ = 120°
Mr = 407.52V = 415.94 (3) Å3
Rhombohedral, R3cZ = 6
a = 5.8025 (2) ÅNeutron radiation, λ = 1.2251 Å
c = 14.2648 (4) ÅT = 440 K
α = 90°
Data collection top
Diffractometer in Debye-Scherrer geometryk =
h = l =
Refinement top
S = 3.0038 parameters
117 reflectionsWeighting scheme based on measured s.u.'s w = 1/(σ2), σ2 = y
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb000.2734 (2)0.0447 (8)
Hf000.0105 (2)0.0041 (4)*0.80
Ti000.0105 (2)0.0041 (4)*0.20
O0.1722 (4)0.3444 (8)0.08330.0248 (3)*
Bond lengths (Å) top
Hf—O2.02O—O3.00
Hf—O2.10O—O2.91
Ti—O2.02Pb—O2.61
Ti—O2.10Pb—O2.92
O—O2.80Pb—O3.22
(5) lead hafnate titanate top
Crystal data top
Hf0.8O3PbTi0.2V = 69.28 (1) Å3
Mr = 407.52Z = 1
Cubic, Pm3mNeutron radiation, λ = 1.2251 Å
Hall symbol: -P 4 2 3T = 520 K
a = 4.1072 (1) Å
Data collection top
Diffractometer in Debye-Scherrer geometryk =
h = l =
Refinement top
S = 2.3733 parameters
39 reflectionsWeighting scheme based on measured s.u.'s w = 1/(σ2), σ2 = y
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb0000.0553 (5)*
Hf0.50.50.50.0037 (4)*0.8
Ti0.50.50.50.0037 (4)*0.2
O0.50.500.0346 (4)
Bond lengths (Å) top
Hf—O2.05O—O2.90
Ti—O2.05Pb—O2.90
 

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