Temperature-dependent neutron powder diffraction evidence for splitting of the cationic sites in ferroelectric PbHf0.4Ti0.6O3

Muller, C.; Baudour, J.-L.; Madigou, V.; Bouree, F.; Kiat, J.-M.; Favotto, C.; Roubin, M.

doi:10.1107/S0108768198005758

Temperature-dependent neutron powder diffraction evidence for splitting of the cationic sites in ferroelectric PbHf_0.4Ti_0.6O₃

C. Muller, J.-L. Baudour, V. Madigou, F. Bouree, J.-M. Kiat, C. Favotto and M. Roubin

Temperature-dependent neutron powder diffraction experiments (diffractometer 3T2-LLB, Saclay, France, λ = 1.227 Å) have been performed on the perovskite-like lead hafnate titanate PbHf_0.4Ti_0.6O₃. This compound belongs to the solid solution denoted PHT, which derives from the well known ferroelectric PZT series. It exhibits a ferroelectric-to-paraelectric phase transition around 620 K, between the low-temperature tetragonal phase and the high-temperature cubic phase. The tetragonal structure of the ferroelectric phase has been refined at 10 and 300 K using a Rietveld-type method: space group P4mm with Z = 1; a_t = 3.999 (1), c_t = 4.120 (1) Å, c/a = 1.030, V = 65.89 Å³ at 10 K; a_t = 4.012 (1) and c_t = 4.100 (1) Å, c/a = 1.022, V = 65.99 Å³ at 300 K. The cubic structure of the paraelectric phase has also been refined at 720 K: space group Pm3m, Z = 1, a_c = 4.046 (1) Å, V = 66.23 Å³. Cation displacements and oxygen-octahedra elongations have been observed as a function of temperature. Evidence for peculiar behaviour associated with the relative shifts of the Hf and Ti atoms (thought until now to be on the same crystallographic site) was found through an anomaly of the mean-square atomic displacements of the Hf/Ti pseudo-nucleus. The PDF Nos for PbHf_0.4Ti_0.6O₃ are 48-49-9 and 48-49-10.

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Supporting information

	Crystallographic Information File (CIF) Contains datablocks global, 1, 2, 3
	Rietveld powder data file (CIF format) Contains datablock 1
	Rietveld powder data file (CIF format) Contains datablock 2
	Rietveld powder data file (CIF format) Contains datablock 3

Computing details top

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

Figures top

(1) lead hafnate titanate top

Crystal data top

Hf_0.4O₃PbTi_0.6	V = 65.89 Å³
M_r = 355.33	Z = 1
Tetragonal, P4mm	Neutron radiation, λ = 1.227 Å
a = 3.999 (1) Å	T = 10 K
c = 4.120 (1) Å	?, ? × ? × ? mm

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 15°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.087	? data points
R_wp = 0.110	Profile function: Pseudo-voigt
R_exp = 0.057	20 parameters
R_Bragg = 0.067	Weighting scheme based on measured s.u.'s w = 1/(σ²), σ² = y
R(F²) = 0.054
χ² = 13.913

Crystal data top

Hf_0.4O₃PbTi_0.6	V = 65.89 Å³
M_r = 355.33	Z = 1
Tetragonal, P4mm	Neutron radiation, λ = 1.227 Å
a = 3.999 (1) Å	T = 10 K
c = 4.120 (1) Å	?, ? × ? × ? mm

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 15°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.087	R(F²) = 0.054
R_wp = 0.110	χ² = 13.913
R_exp = 0.057	? data points
R_Bragg = 0.067	20 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Pb	0	0	0	0.008 (1)*
Hf	0.5	0.5	0.539 (3)	0.003 (3)*	0.42
Ti	0.5	0.5	0.499 (3)	0.003 (3)*	0.58
O1	0.5	0.5	0.095 (2)	0.011 (1)*
O2	0.5	0	0.615 (2)	0.011 (1)*

Bond lengths (Å) top

Hf—O1	1.83	O2—O2	2.83
Hf—O1	2.29	O2—O1	2.93
Hf—O2	2.02	O2—O1	2.81
Ti—O1	1.66	Pb—O1	2.85
Ti—O1	2.46	Pb—O2	2.55
Ti—O2	2.06	Pb—O2	3.23

(2) lead hafnate titanate top

Crystal data top

Hf_0.4O₃PbTi_0.6	V = 65.99 Å³
M_r = 355.33	Z = 1
Tetragonal, P4mm	Neutron radiation, λ = 1.227 Å
a = 4.012 (1) Å	T = 300 K
c = 4.100 (1) Å	?, ? × ? × ? mm

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 15°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.073	? data points
R_wp = 0.095	Profile function: Pseudo-voigt
R_exp = 0.047	20 parameters
R_Bragg = 0.058	Weighting scheme based on measured s.u.'s w = 1/(σ²), σ² = y
R(F²) = 0.051
χ² = 16.402

Crystal data top

Hf_0.4O₃PbTi_0.6	V = 65.99 Å³
M_r = 355.33	Z = 1
Tetragonal, P4mm	Neutron radiation, λ = 1.227 Å
a = 4.012 (1) Å	T = 300 K
c = 4.100 (1) Å	?, ? × ? × ? mm

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 15°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.073	R(F²) = 0.051
R_wp = 0.095	χ² = 16.402
R_exp = 0.047	? data points
R_Bragg = 0.058	20 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Pb	0	0	0	0.016 (1)*
Hf	0.5	0.5	0.535 (2)	0.008 (3)*	0.42
Ti	0.5	0.5	0.495 (4)	0.008 (3)*	0.58
O1	0.5	0.5	0.079 (2)	0.018 (1)*
O2	0.5	0	0.597 (1)	0.018 (1)*

Bond lengths (Å) top

Hf—O1	1.87	O2—O2	2.84
Hf—O1	2.23	O2—O1	2.92
Hf—O2	2.02	O2—O1	2.82
Ti—O1	1.71	Pb—O1	2.86
Ti—O1	2.39	Pb—O2	2.60
Ti—O2	2.05	Pb—O2	3.16

(3) lead hafnate titanate top

Crystal data top

Hf_0.4O₃PbTi_0.6	V = 66.23 Å³
M_r = 355.33	Z = 1
Cubic, Pm3m	Neutron radiation, λ = 1.227 Å
Hall symbol: -P 4 2 3	T = 720 K
a = 4.046 (1) Å	?, ? × ? × ? mm

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 23°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.046	? data points
R_wp = 0.057	Profile function: Pseudo-voigt
R_exp = 0.055	13 parameters
R_Bragg = 0.028	Weighting scheme based on measured s.u.'s w = 1/(σ²), σ² = y
R(F²) = 0.066
χ² = 1.103

Crystal data top

Hf_0.4O₃PbTi_0.6	Z = 1
M_r = 355.33	Neutron radiation, λ = 1.227 Å
Cubic, Pm3m	T = 720 K
a = 4.046 (1) Å	?, ? × ? × ? mm
V = 66.23 Å³

Data collection top

Diffractometer in Debye-Scherrer geometry

2θ_min = 23°, 2θ_max = 109°, 2θ_step = 0.05°

Refinement top

R_p = 0.046	R(F²) = 0.066
R_wp = 0.057	χ² = 1.103
R_exp = 0.055	? data points
R_Bragg = 0.028	13 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Pb	0	0	0	0.052 (4)*
Hf	0.5	0.5	0.5	0.014 (5)*	0.42
Ti	0.5	0.5	0.54	0.014 (5)*	0.097
O	0.5	0.5	0	0.032 (2)*

Bond lengths (Å) top

Hf—O	2.02	Ti—O	2.03
Ti—O	1.86	O—O	2.86
Ti—O	2.18	Pb—O	2.86

Experimental details

	(1)	(2)	(3)
Crystal data
Chemical formula	Hf_0.4O₃PbTi_0.6	Hf_0.4O₃PbTi_0.6	Hf_0.4O₃PbTi_0.6
M_r	355.33	355.33	355.33
Crystal system, space group	Tetragonal, P4mm	Tetragonal, P4mm	Cubic, Pm3m
Temperature (K)	10	300	720
a, b, c (Å)	3.999 (1), 3.999 (1), 4.120 (1)	4.012 (1), 4.012 (1), 4.100 (1)	4.046 (1), 4.046 (1), 4.046 (1)
α, β, γ (°)	90, 90, 90	90, 90, 90	90, 90, 90
V (Å³)	65.89	65.99	66.23
Z	1	1	1
Radiation type	Neutron, λ = 1.227 Å	Neutron, λ = 1.227 Å	Neutron, λ = 1.227 Å
Specimen shape, size (mm)	?, ? × ? × ?	?, ? × ? × ?	?, ? × ? × ?

Data collection
Diffractometer	Diffractometer in Debye-Scherrer geometry	Diffractometer in Debye-Scherrer geometry	Diffractometer in Debye-Scherrer geometry
Specimen mounting	?	?	?
Data collection mode	?	?	?
Scan method	?	?	?
2θ values (°)	2θ_min = 15 2θ_max = 109 2θ_step = 0.05	2θ_min = 15 2θ_max = 109 2θ_step = 0.05	2θ_min = 23 2θ_max = 109 2θ_step = 0.05

Refinement
R factors and goodness of fit	R_p = 0.087, R_wp = 0.110, R_exp = 0.057, R_Bragg = 0.067, R(F²) = 0.054, χ² = 13.913	R_p = 0.073, R_wp = 0.095, R_exp = 0.047, R_Bragg = 0.058, R(F²) = 0.051, χ² = 16.402	R_p = 0.046, R_wp = 0.057, R_exp = 0.055, R_Bragg = 0.028, R(F²) = 0.066, χ² = 1.103
No. of data points	?	?	?
No. of parameters	20	20	13
No. of restraints	?	?	?

Computer programs: Fullprof, CaRIne, version 3.0.

Format		BIBTeX
		EndNote
		RefMan
		Refer
		Medline
		CIF
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Format		BIBTeX
		EndNote
		RefMan
		Refer
		Medline
		CIF
		SGML
		Text
		Plain Text

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