Structural elucidation of the Bi_2(n + 2)Mo_nO_6(n + 1) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopy

The cationic framework structure of a whole new family of compounds with the general formula Bi_2(n + 2)Mo_nO_6(n + 1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi₁₀Mo₃O₂₄. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common δ-Bi₂O₃ fluorite-type framework, inside of which are distributed ribbons of {MoO₄} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO₄} tetrahedra along a depending on the family member (n value). These {MoO₄} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi₁₂O₁₄] columnar structural-type phase Bi[Bi₁₂O₁₄][MoO₄]₄[VO₄]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi₂MoO₆, the n = ∞ end member. All these compounds are good oxygen-ion conductors.

Computing details

(Bi816Mo6O42)

Crystal data

Monoclinic, P21	c = 8.6340 (1) Å
a = 19.9850 (1) Å	β = 101.0200 (1)°
b = 5.6320 (1) Å

Data collection

h = →	l = →
k = →

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

	x	y	z	Biso*/Beq
Bi1	0.5227	0.5000	0.1591
Bi2	0.3864	0.0000	0.2045
Bi3	0.2500	0.5000	0.2500
Bi4	0.1136	0.0000	0.3182
Bi5	0.9773	0.5000	0.3409
Bi6	0.8409	0.0000	0.3864
Bi7	0.7045	0.5000	0.4318
Bi8	0.5682	0.0000	0.4773
Mo1	0.9318	0.0000	0.0227
Mo2	0.7955	0.5000	0.0682
Mo3	0.6591	0.0000	0.1136

(Bi10Mo3new)

Crystal data

Monoclinic, C2	c = 8.6817 (1) Å
a = 23.7282 (1) Å	β = 95.8700 (1)°
b = 5.6491 (1) Å

Data collection

h = →	l = →
k = →

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

	x	y	z	Biso*/Beq
Bi1	0.7692	0.0000	0.1538
Bi2	0.6538	0.5000	0.2308
Bi3	0.5385	0.0000	0.3077
Bi5	0.3077	0.0000	0.4615
Bi_4	0.4231	0.5000	0.3846
Mo1	0.0000	0.0000	0.0000
Mo2	0.8846	0.5000	0.0769

(Bi12Mo4O30)

Crystal data

Monoclinic, P21	c = 8.6620 (1) Å
a = 14.5300 (1) Å	β = 97.9790 (1)°
b = 5.6480 (1) Å

Data collection

h = →	l = →
k = →

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

	x	y	z	Biso*/Beq
Bi1	0.5313	0.5000	0.1563
Bi2	0.3438	0.0000	0.2188
Bi3	0.1563	0.5000	0.2813
Bi4	0.9688	0.0000	0.3438
Bi5	0.7813	0.5000	0.4063
Bi6	0.5938	0.0000	0.4688
Mo1	0.9063	0.5000	0.0313
Mo2	0.7188	0.0000	0.0938

(Bi14Mo5O36)

Crystal data

Monoclinic, C2	c = 8.6433 (1) Å
a = 34.4760 (1) Å	β = 99.6900 (1)°
b = 5.6414 (1) Å

Data collection

h = →	l = →
k = →

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

	x	y	z	Biso*/Beq
Bi_4	0.5263	0.0000	0.3158
Bi1	0.7632	0.5000	0.1579
Bi2	0.6842	0.0000	0.2105
Bi3	0.6053	0.5000	0.2632
Bi5	0.4474	0.5000	0.3684
Bi6	0.3684	0.0000	0.4211
Bi7	0.2895	0.5000	0.4737
Mo1	0.0000	0.0000	0.0000
Mo2	0.9211	0.5000	0.0526
Mo3	0.8421	0.0000	0.1053