The tetragonal phase of Na_0.5Bi_0.5TiO₃ - a new variant of the perovskite structure

The structure of the tetragonal phase of the A-site-substituted perovskite sodium bismuth titanate, Na_0.5Bi_0.5TiO₃, has been determined by neutron powder diffraction at 698 K. The structure was refined in space group P4bm with a (= b) = 5.5191 (1), c = 3.9085 (1) Å, V = 119.055 (5) Å³, Z = 2 and D_x = 5.91 Mg m^-3. The structure exhibits an unusual combination of in-phase (a⁰a⁰c⁺) tilts and antiparallel cation displacements along the polar c axis, which results in a new variant of the perovskite structure.

Computing details

Figures

sodium bismuth titanate

Crystal data

Bi0.5Na0.5O3Ti	V = 119.06 (1) Å^3
Mr = 211.88	Z = 2
Tetragonal, P4bm	Dx = 5.91 Mg m^−3
Hall symbol: P 4 -2ab	? radiation, λ = 1.595 Å
a = 5.5191 (1) Å	T = 698 K
c = 3.9085 (5) Å	?, ? × ? × ? mm

Data collection

2θmin = 21.803°, 2θmax = 140.003°, 2θstep = 0.05°

Refinement

Rp = ?	? data points
Rwp = ?	39 parameters
Rexp = ?
χ^2 = 0.005

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Na1	0.0	0.5	0.523 (4)	0.05117	.5
Bi2	0.0	0.5	0.523 (4)	0.07167	.5
Ti3	0.0	0.0	0.0	0.01591
O4	0.0	0.0	0.515 (4)	0.04778
O5	0.270 (3)	0.230 (3)	0.026 (4)	0.03766

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.048 (5)	0.048 (5)	0.058 (5)	−0.004 (2)	0.0	0.0
Bi2	0.076 (4)	0.076 (4)	0.064 (8)	−0.003 (2)	0.0	0.0
Ti3	0.021 (2)	0.021 (2)	0.006 (4)	0.0	0.0	0.0
O4	0.068 (2)	0.068 (2)	0.008 (2)	0.0	0.0	0.0
O5	0.026 (1)	0.026 (1)	0.061 (2)	−0.012 (2)	0.009 (4)	−0.009 (4)

Geometric parameters (Å, º)

Na/Bi—O(1)	2.7598 (1)	Na/Bi—O(2)	2.6618 (1)
Na/Bi—O(2)	2.8666 (1)	Na/Bi—Ti	3.4343 (1)
Na/Bi—O(2)	2.8822 (1)	Na/Bi—Ti	3.3302 (1)
Na/Bi—O(2)	2.6449 (1)
Ti—Na/Bi—Ti	111.919 (2)	Ti—Na/Bi—O(2)	36.053 (1)
Ti—Na/Bi—Ti	71.739 (1)	Ti—Na/Bi—O(2)	143.977 (1)
Ti—Na/Bi—O(1)	34.748 (1)	Ti—Na/Bi—O(2)	88.951 (2)
Ti—Na/Bi—O(1)	146.667 (1)	Ti—Na/Bi—O(2)	90.778 (2)
Ti—Na/Bi—O(1)	90.396 (1)