X-ray powder diffraction and electron diffraction studies of the thortveitite-related L phase, (Zn,Mn)₂V₂O₇

The phase designated γ-Zn₃(VO₄)₂ reported as a minor second phase in zinc oxide-based varistor materials doped with vanadium oxide and manganese oxide is shown to be the L phase, (Zn_1 − xMn_x)₂V₂O₇ (0.188 < x < 0.538), in the pseudo-binary Mn₂V₂O₇–Zn₂V₂O₇ system. Analysis of X-ray powder diffraction patterns and electron diffraction patterns of this phase shows that the previously published a, c and β values for this thortveitite-related phase are incorrect. Instead, Rietveld refinement of the X-ray powder pattern of the L phase shows that it has a monoclinic C lattice with Z = 6, with a  =  10.3791 (1), b = 8.5557 (1), c = 9.3539 (1) Å and β = 98.467 (1)°. Although prior convergent-beam electron diffraction work of `γ-Zn₃(VO₄)₂' confirmed the C Bravais lattice, the space group was found to be Cm rather than C2/m, the difference perhaps arising from the inability of the X-rays to detect small displacements of oxygen. Attempts to refine the structure in Cm did not produce improved R factors. The relationship between the crystal structure of the L phase and the high-temperature C2/m β′-Zn₂V₂O₇ thortveitite-type solid solution is discussed.

Computing details

Figures

(I)

Crystal data

Mn0.6O7V2Zn1.4	V = 821.58 (2) Å^3
Mr = 338.37	Z = 6
Monoclinic, C2/m	Dx = 4.10 Mg m^−3
a = 10.37908 (11) Å	Cu Kα radiation, λ = 1.5418 Å
b = 8.55572 (9) Å	T = 298 K
c = 9.35394 (10) Å	black-brown
β = 98.4667 (9)°	flat sheet, 20 × 20 mm

Data collection

Bruker D8 diffractometer

2θmin = 7.986°, 2θmax = 157.980°, 2θstep = 0.018°

Refinement

Rp = 0.076	? data points
Rwp = 0.099	53 parameters
Rexp = 0.075	(Δ/σ)max = 0.001
R(F) = 0.032	Background function: One on X 1172.905 Chebychev polynomial, Coefficient 0 58.91392 1 37.15686 2 1.077047 3 11.79921 4 -2.054791 5 -3.935534 6 5.044208 7 -0.2344829 8 1.70655 9 0.434558 10 2.996575
χ^2 = 1.322

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

	x	y	z	Biso*/Beq	Occ. (<1)
Zn1	0.3463 (2)	0.8183 (2)	0.20169 (19)	0.24 (4)*	0.7
Zn2	0	0.8210 (4)	0.5	0.24 (4)*	0.7
V1	0.0496 (3)	0	0.1870 (4)	0.01 (3)*
V2	0.3732 (3)	0	0.8855 (3)	0.01 (3)*
V3	0.6933 (4)	0	0.4888 (4)	0.01 (3)*
O1a	0.3838 (10)	0	0.6859 (10)	0.17 (6)*
O1b	0	0	0	0.17 (6)*
O2a	0.0017 (7)	0.1663 (10)	0.7449 (7)	0.17 (6)*
O2b	0.2812 (8)	0.1537 (9)	0.8906 (7)	0.17 (6)*
O2c	0.3497 (8)	0.1652 (9)	0.4243 (7)	0.17 (6)*
O3a	0.1349 (11)	0	0.5033 (11)	0.17 (6)*
O3b	0.4402 (13)	0	0.1005 (11)	0.17 (6)*
O3c	0.2153 (13)	0	0.2048 (11)	0.17 (6)*
Mn1	0.3463 (2)	0.8183 (2)	0.20169 (19)	0.24 (4)*	0.3
Mn2	0	0.8210 (4)	0.5	0.24 (4)*	0.3

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.00306	0.00306	0.00306	0.000000	0.000000	0.000000
Zn2	0.00306	0.00306	0.00306	0.000000	0.000000	0.000000
V1	0.00013	0.00013	0.00013	0.000000	0.000000	0.000000
V2	0.00013	0.00013	0.00013	0.000000	0.000000	0.000000
V3	0.00013	0.00013	0.00013	0.000000	0.000000	0.000000
O1a	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O1b	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O2a	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O2b	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O2c	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O3a	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O3b	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
O3c	0.00210	0.00210	0.00210	0.000000	0.000000	0.000000
Mn1	0.00306	0.00306	0.00306	0.000000	0.000000	0.000000
Mn2	0.00306	0.00306	0.00306	0.000000	0.000000	0.000000

Geometric parameters (Å, º)

Zn1—O2b^i	2.035 (8)	V1—O2a^viii	1.677 (8)
Zn1—O2a^i	2.049 (8)	V1—O3c	1.704 (14)
Zn1—O3c^ii	2.068 (9)	V1—O1b	1.7495
Zn1—O2c^iii	2.082 (7)	V2—O2b	1.630 (8)
Zn1—O3b^ii	2.130 (9)	V2—O2b^ix	1.630 (8)
Zn2—O3a^ii	2.073 (8)	V2—O1a	1.887 (10)
Zn2—O3a^iv	2.073 (8)	V2—O3b^x	1.922 (13)
Zn2—O2c^v	2.094 (8)	V2—O3b^xi	2.028 (10)
Zn2—O2c^i	2.094 (8)	V3—O1a^x	1.710 (9)
Zn2—O2a^vi	2.291 (7)	V3—O2c^x	1.722 (8)
Zn2—O2a^iii	2.291 (7)	V3—O2c^xii	1.722 (8)
V1—O2a^vii	1.677 (8)	V3—O3a^x	1.774 (12)
O2a^i—Zn1—O2b^i	95.4 (2)	O2a^viii—V1—O2a^vii	116.1 (6)
O3c^ii—Zn1—O2a^i	163.3 (3)	O3c—V1—O2a^viii	109.6 (3)
O3c^ii—Zn1—O2b^i	98.0 (2)	O3c—V1—O2a^vii	109.6 (3)
O2c^iii—Zn1—O3c^ii	81.3 (3)	O1b—V1—O3c	104.0 (4)
O2c^iii—Zn1—O2a^i	84.3 (2)	O1b—V1—O2a^viii	108.5 (2)
O2c^iii—Zn1—O2b^i	112.7 (2)	O1b—V1—O2a^vii	108.5 (2)
O3b^ii—Zn1—O2c^iii	117.0 (3)	O2b^ix—V2—O2b	107.6 (6)
O3b^ii—Zn1—O3c^ii	78.6 (4)	O1a—V2—O2b^ix	98.5 (2)
O3b^ii—Zn1—O2a^i	100.7 (4)	O1a—V2—O2b	98.5 (2)
O3b^ii—Zn1—O2b^i	128.9 (3)	O3b^x—V2—O1a	82.1 (4)
O3a^iv—Zn2—O3a^ii	84.7 (5)	O3b^x—V2—O2b^ix	125.9 (3)
O2c^v—Zn2—O3a^iv	89.9 (2)	O3b^x—V2—O2b	125.9 (3)
O2c^v—Zn2—O3a^ii	160.6 (3)	O3b^xi—V2—O3b^x	74.8 (6)
O2c^i—Zn2—O2c^v	100.9 (5)	O3b^xi—V2—O1a	156.9 (5)
O2c^i—Zn2—O3a^iv	160.6 (3)	O3b^xi—V2—O2b^ix	95.1 (3)
O2c^i—Zn2—O3a^ii	89.9 (2)	O3b^xi—V2—O2b	95.1 (3)
O2a^vi—Zn2—O2c^i	105.3 (3)	O2c^x—V3—O1a^x	109.5 (2)
O2a^vi—Zn2—O2c^v	78.3 (3)	O2c^xii—V3—O2c^x	110.4 (5)
O2a^vi—Zn2—O3a^iv	92.5 (3)	O2c^xii—V3—O1a^x	109.5 (2)
O2a^vi—Zn2—O3a^ii	83.4 (3)	O3a^x—V3—O2c^xii	108.0 (3)
O2a^iii—Zn2—O2a^vi	174.6 (4)	O3a^x—V3—O2c^x	108.0 (3)
O2a^iii—Zn2—O2c^i	78.3 (3)	O3a^x—V3—O1a^x	111.4 (5)
O2a^iii—Zn2—O2c^v	105.3 (3)	V2—O1a—V3^x	149.1 (6)
O2a^iii—Zn2—O3a^iv	83.4 (3)	V1—O1b—V1^xiii	180.000
O2a^iii—Zn2—O3a^ii	92.5 (3)

Symmetry codes: (i) −x+1/2, y+1/2, −z+1; (ii) x, y+1, z; (iii) x, −y+1, z; (iv) −x, y+1, −z+1; (v) x−1/2, y+1/2, z; (vi) −x, −y+1, −z+1; (vii) −x, y, −z+1; (viii) −x, −y, −z+1; (ix) x, −y, z; (x) −x+1, y, −z+1; (xi) x, y, z+1; (xii) −x+1, −y, −z+1; (xiii) −x, y, −z.