A novel perovskite-like Ta-bronze KTa_1+zO₃: preparation, stoichiometry, conductivity and crystal structure studies

A new cubic Ta-bronze (1) KTaO₃ [z ≃ 0.107 (3)] was obtained on a cathode by molten salt electrolysis of the system K₂TaOF₅–K₃TaO₂F₄–(KF + NaF + LiF)_eutectic. Black, metallic cubic crystals of (1) are formed together with tetragonal β-Ta. The perovskite-like crystal structure of (1) [a = 4.005 (1) Å, space group ] was refined with anharmonic displacement parameters for Ta and K atoms and anisotropic displacement parameters for a split O-atom position [KM4CCD diffractometer; λ(Mo Kα); 3320 measured reflections with I > 3σ(I); R = 0.0095, wR = 0.0065, Δρ_min = −0.91 e Å⁻³, Δρ_max = 0.65 e Å⁻³]. Defects in the O and K atomic positions were found. (1) is a semiconductor in the temperature range 4–300 K, whereas the well studied and closely related colourless transparent crystals KTa⁺⁵O₃ (2) are dielectric. Differences in the properties of (1) and (2) are assumed to be connected with the existence of Ta dumb-bells statistically distributed into the KTaO₃ matrix.

Computing details

Figures

(I)

Crystal data

K0.934O2.94Ta	Dx = 6.835 Mg m^−3
Mr = 264.5	Mo Kα radiation, λ = 0.71073 Å
Cubic, Pm3m	Cell parameters from 3320 reflections
Hall symbol: -P 4 2 3	θ = 5.1–71.0°
a = 4.0050 (4) Å	µ = 43.97 mm^−1
V = 64.24 (1) Å^3	T = 295 K
Z = 1	Box, black metallic
F(000) = 113	0.05 × 0.05 × 0.03 mm

Data collection

KM4 diffractometer	148 reflections with 3
CCD scans	Rint = 0.025
Absorption correction: gaussian integration ?	θmax = 71.3°, θmin = 5.1°
Tmin = 0.290, Tmax = 0.770	h = −10→10
3320 measured reflections	k = −9→10
148 independent reflections	l = −10→8

Refinement

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/σ^2(F)
R[F^2 > 2σ(F^2)] = 0.009	(Δ/σ)max = 0.014
wR(F^2) = 0.006	Δρmax = 0.82 e Å^−3
S = 3.05	Δρmin = −0.86 e Å^−3
148 reflections	Extinction correction: B-C type 1 Gaussian isotropic
16 parameters	Extinction coefficient: 0.014922

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ta	0	0	0	0.0065 (1)
K	0.5	0.5	0.5	0.0042 (2)	0.959 (1)
O	0.515 (1)	0	0	0.00543 (13)	0.493 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ta	0.0065 (1)	0.0065 (1)	0.0065 (1)	0	0	0
K	0.004208	0.0042 (2)	0.0042 (2)	0	0	0
O	0.0006 (2)	0.0078 (2)	0.0078 (2)	0	0	0

Bond lengths (Å)

Ta—O^i	1.944	K—O^xxv	2.8326
Ta—O	2.061	K—O^xxvi	2.8326
Ta—O^ii	2.061	K—O^xi	2.8326
Ta—O^iii	1.944	K—O^xxvii	2.8326
Ta—O^iv	1.944	K—O^xxviii	2.8326
Ta—O^v	2.061	K—O^xxix	2.8326
Ta—O^vi	2.061	O—Ta	2.061
Ta—O^vii	1.944	O—Ta^xxx	1.944
Ta—O^viii	1.944	O—K^xxxi	2.8326
Ta—O^ix	2.061	O—K^xxxii	2.8326
Ta—O^x	2.061	O—K^xxxiii	2.8326
Ta—O^xi	1.944	O—K	2.8326
K—O	2.8326	O—O^iii	0.117
K—O^xii	2.8326	O—O^iv	2.8332
K—O^xiii	2.8326	O—O^v	2.9147
K—O^xiv	2.8326	O—O^xxxiv	2.7492
K—O^iii	2.8326	O—O^xix	2.8332
K—O^xv	2.8326	O—O^vi	2.9147
K—O^xvi	2.8326	O—O^vii	2.8332
K—O^xvii	2.8326	O—O^xxxv	2.8332
K—O^v	2.8326	O—O^xxii	2.7492
K—O^xviii	2.8326	O—O^viii	2.8332
K—O^xix	2.8326	O—O^ix	2.9147
K—O^xx	2.8326	O—O^xxxvi	2.7492
K—O^vii	2.8326	O—O^xxv	2.8332
K—O^xxi	2.8326	O—O^x	2.9147
K—O^xxii	2.8326	O—O^xi	2.8332
K—O^xxiii	2.8326	O—O^xxxvii	2.8332
K—O^ix	2.8326	O—O^xxviii	2.7492
K—O^xxiv	2.8326

Symmetry codes: (i) x−1, y, z; (ii) −x, −y, −z; (iii) −x+1, −y, −z; (iv) −y, x−1, z; (v) −y, x, z; (vi) y, −x, −z; (vii) y, −x+1, −z; (viii) z, −y, x−1; (ix) z, −y, x; (x) −z, y, −x; (xi) −z, y, −x+1; (xii) x, y, z+1; (xiii) x, y+1, z; (xiv) x, y+1, z+1; (xv) −x+1, −y, −z+1; (xvi) −x+1, −y+1, −z; (xvii) −x+1, −y+1, −z+1; (xviii) −y, x, z+1; (xix) −y+1, x, z; (xx) −y+1, x, z+1; (xxi) y, −x+1, −z+1; (xxii) y+1, −x+1, −z; (xxiii) y+1, −x+1, −z+1; (xxiv) z, −y+1, x; (xxv) z+1, −y, x; (xxvi) z+1, −y+1, x; (xxvii) −z, y+1, −x+1; (xxviii) −z+1, y, −x+1; (xxix) −z+1, y+1, −x+1; (xxx) x+1, y, z; (xxxi) x, y−1, z−1; (xxxii) x, y−1, z; (xxxiii) x, y, z−1; (xxxiv) −y+1, x−1, z; (xxxv) y+1, −x, −z; (xxxvi) z+1, −y, x−1; (xxxvii) −z+1, y, −x.