research papers
A new polymorph of Pb2BiVO6 was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions α → β and β → δ were identified in the mother phase; the high-temperature form δ-Pb2BiVO6 eventually decomposes at 753 K to a mixture of Pb4BiVO8 and the high-temperature form of PbBiVO5 before showing recombination at 923 K. β-Pb2BiVO6 has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of β-Pb2BiVO6 by TEM diffraction studies confirmed the lattice and incommensurate modulation character. Log σ = f(T−1) dependences for Pb2BiVO6-related materials (6% M-for-V-substituted compositions; M = Cr, Mn, P) are reported, which allow the characterization (Ea and isothermal σ values) of the β- as well as the δ- and α-Pb2BiVO6 varieties.
Keywords: polymorphism; phase stabilization; incommensurately modulated structure; oxide ionic conduction.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768109020898/bp5019sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108768109020898/bp5019Isup2.fcf |
Computing details top
Data collection: KM4B8 (Kuma Diffraction Ltd., 1996); cell refinement: KM4B8 (Kuma Diffraction Ltd., 1996); data reduction: Jana2000 (Petricek & Dusek, 2000); program(s) used to solve structure: SIR97 (Altomare et al., 1997); program(s) used to refine structure: Jana2006 (Petricek, Dusek & Palatinus, 2006); molecular graphics: Diamond (Brandenburg, 1999); software used to prepare material for publication: Jana2006 (Petricek, Dusek & Palatinus, 2006).
(I) top
Crystal data top
BiO6Pb2V | V = 655.37 (6) Å3 |
Mr = 770.3 | Z = 4 |
Monoclinic, P21/m(0β0)s0† | F(000) = 1272 |
q = 0.23382b* | Dx = 7.804 Mg m−3 |
Hall symbol: -P 2yb | Mo Kα radiation, λ = 0.71073 Å |
a = 15.0501 (5) Å | µ = 81.17 mm−1 |
b = 5.9011 (3) Å | T = 298 K |
c = 7.5322 (5) Å | Platelet, black |
β = 101.5657° | 0.21 × 0.12 × 0.05 mm |
† Symmetry operations: (1) x1, x2, x3, x4; (2) −x1, x2+1/2, −x3, x4+1/2; (3) −x1, −x2, −x3, −x4; (4) x1, −x2+1/2, x3, −x4+1/2. |
Data collection top
Bruker CCD diffractometer | 24247 independent reflections |
Radiation source: X-ray tube | 4097 reflections with I > 3σ(I) |
Graphite monochromator | Rint = 0.152 |
ω–scans | θmax = 40.3°, θmin = 1.4° |
Absorption correction: analytical Sadabs (Sheldrick 2004) | h = −25→27 |
Tmin = 0.301, Tmax = 1 | k = −11→11 |
110335 measured reflections | l = −13→13 |
Refinement top
Refinement on F | 0 restraints |
R[F2 > 2σ(F2)] = 0.036 | 1 constraint |
wR(F2) = 0.032 | Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2) |
S = 1.07 | (Δ/σ)max < 0.001 |
4097 reflections | Δρmax = 3.44 e Å−3 |
189 parameters | Δρmin = −6.04 e Å−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | Occ. (<1) | |
Bi1 | 0.80070 (4) | 0.25 | 0.42521 (7) | 0.02056 (19) | |
Bi2 | 0.71083 (4) | 0.75 | 0.64948 (8) | 0.01813 (19) | |
Pb1 | 0.95280 (4) | 0.75 | 0.70209 (9) | 0.0196 (2) | |
Pb2 | 0.55636 (4) | 0.25 | 0.37273 (8) | 0.01834 (19) | |
Pb3 | 0.84761 (5) | 0.25 | 0.91902 (8) | 0.0207 (2) | |
Pb4 | 0.64789 (4) | 0.75 | 0.15756 (8) | 0.0254 (2) | |
O1 | 0.6787 (4) | 0.5092 (13) | 0.4078 (8) | 0.025 (3) | |
O2 | 0.8346 (4) | 0.9943 (14) | 0.6793 (9) | 0.026 (3) | |
V1a | 0.59555 (16) | 0.2348 (10) | 0.8701 (3) | 0.0171 (9) | 0.5 |
O11a | 0.5883 (7) | 0.233 (4) | 1.0878 (16) | 0.031 (4)* | 0.5 |
O12a | 0.6925 (9) | 0.340 (3) | 0.8386 (19) | 0.048 (5)* | 0.5 |
O13a | 0.5895 (11) | −0.017 (3) | 0.778 (2) | 0.041 (5)* | 0.5 |
O14a | 0.5093 (9) | 0.381 (3) | 0.7476 (18) | 0.035 (4)* | 0.5 |
V2a | 0.1185 (4) | 0.25 | 0.8139 (8) | 0.0197 (13) | 0.5 |
O21a | 0.0348 (13) | 0.25 | 0.928 (3) | 0.051 (4)* | 0.5 |
O22a | 0.0827 (13) | 0.25 | 0.595 (2) | 0.059 (5)* | 0.5 |
O23a | 0.1894 (7) | 0.4721 (14) | 0.8728 (19) | 0.041 (3)* | 0.5 |
V2b | 0.1004 (4) | 0.25 | 0.7768 (8) | 0.0197 (13) | 0.5 |
O21b | 0.0455 (13) | 0.25 | 0.947 (3) | 0.051 (4)* | 0.5 |
O22b | 0.2104 (11) | 0.25 | 0.844 (3) | 0.059 (5)* | 0.5 |
O23b | 0.0695 (9) | 0.0279 (14) | 0.6357 (15) | 0.041 (3)* | 0.5 |
Atomic displacement parameters (Å2) top
U11 | U22 | U33 | U12 | U13 | U23 | |
Bi1 | 0.0194 (3) | 0.0219 (3) | 0.0200 (3) | 0 | 0.0029 (2) | 0 |
Bi2 | 0.0166 (3) | 0.0161 (3) | 0.0215 (3) | 0 | 0.0032 (2) | 0 |
Pb1 | 0.0152 (3) | 0.0216 (4) | 0.0214 (3) | 0 | 0.0021 (2) | 0 |
Pb2 | 0.0168 (3) | 0.0201 (3) | 0.0179 (3) | 0 | 0.0030 (2) | 0 |
Pb3 | 0.0245 (4) | 0.0198 (3) | 0.0169 (3) | 0 | 0.0019 (3) | 0 |
Pb4 | 0.0235 (3) | 0.0310 (4) | 0.0209 (3) | 0 | 0.0023 (2) | 0 |
O1 | 0.028 (4) | 0.017 (4) | 0.028 (5) | −0.004 (4) | −0.001 (3) | −0.003 (4) |
O2 | 0.026 (4) | 0.027 (4) | 0.024 (5) | −0.004 (3) | 0.001 (3) | −0.002 (4) |
V1a | 0.0165 (13) | 0.0183 (18) | 0.0167 (16) | −0.0011 (16) | 0.0043 (11) | 0.0015 (18) |
V2a | 0.027 (2) | 0.0155 (15) | 0.017 (2) | 0 | 0.0071 (17) | 0 |
V2b | 0.017 (2) | 0.0155 (15) | 0.027 (2) | 0 | 0.0073 (17) | 0 |