Crystal structure of bismuth gallium aluminium oxide, Bi2(GaxAl1–x)4O9, x = 0.4, 0.6, 0.8

Abstract

Al2.4Bi2Ga1.6O9, orthorhombic, Pbam (no. 55), a = 7.79697(7) A, b = 8.16575(7) A, c = 5.75442(5) A, V = 366.4 A, Z = 2, Rw(P) = 0.067, R(P) = 0.048, R(I) = 0.022, T = 293 K. Al1.6Bi2Ga2.4O9, orthorhombic, Pbam (no. 55), a = 7.83752(8) A, b = 8.20096(8) A, c = 5.79475(6) A, V = 372.5 A, Z = 2, Rw(P) = 0.081, R(P) = 0.057, R(I) = 0.031, T = 293 K. Al0.8Bi2Ga3.2O9, orthorhombic, Pbam (no. 55), a = 7.88345(6) A, b = 8.24579(6) A, c = 5.84335(4) A, V = 379.9 A, Z = 2, Rw(P) = 0.075, R(P) = 0.054, R(I) = 0.028, T = 293 K. Source of material Solid solution samples of mullite type in the system Bi2(GaxAl1–x)4O9 (0.0 ≤ x ≤ 1.0) were prepared by glycerinenitrate method. Equimolar amounts of aluminum nitrate nonahydrate, gallium nitrate heptahydrate, bismuth nitrate pentahydrate were used as reactants. The water content in the reactants wasmeasured using TG (SetaramSetsys evolution 1750). The reactants were dissolved at 353 K in glycerine (metal : glycerine = 1.:.5) and heated at 393 K to form an amorphous gel. The dried gel was heated in an open Pt crucible at 1073 K for about 30.h to get final product. EDXS analysis of the polished samples showed the chemical compositions of the products in good agreement with the nominal compositions. Discussion Bi2(GaxAl1–x)4O9 (0.0 ≤ x ≤ 1.0) is a new solid solution, which is isotype to Bi2(FexAl1–x)4O9 (0.0 ≤ x ≤ 1.0) [1,2] and Bi2(FexGa1–x)4O9 (0.0 ≤ x ≤ 1.0) [3,4]. M (M = Ga/Al) ions are octahedrally (MO6) and tetrahedrally (MO4) coordinated with oxygen atoms. MO6 octahedra are edge-shared along [001] and are inter-linked by dimer (M2O7) of MO4 tetrahedra, forming five-membered rings of two octahedra (MO6) and three tetrahedra (MO4). As a result, a channel-like structure is formed. Bi ions are located in the channels. The BiO4 groups alternate with the planes ofM2O7 units. Structure refinements reveal a preferential occupation of Ga in tetrahedral site (4h), which is similar to the results obtained for Bi2(FexGa1–x)4O9 (x = 0.50) [3]. The refinement of the occupation parameters and EDXS analysis of the samples with nominal compositions x = 0.4, 0.6, 0.8 give the x values of 0.41(1), 0.59(1), 0.79(1) and 0.39(2), 0.59(2), 0.80(2), respectively. The lattice parameters of Bi2(GaxAl1–x)4O9 system vary linearly (a/A = 0.209x + 7.7194, b/A = 0.184x + 8.1036, c/A = 0.202x + 5.6835) as function of nominal composition, x. Z. Kristallogr. NCS 225 (2010) 1-2 / DOI 10.1524/ncrs.2010.0001 1 © by Oldenbourg Wissenschaftsverlag, Munchen Powder: white, particle size < 63 .m Wavelength: 1.78896 A .: 23.7 cm−1 Diffractometer: Stoe STADI P 2,max, stepwidth: 114.98°, 0.02° N(hkl)measured: 185 N(param)refined: 29 Programs: DIAMOND [5], TOPAS [6] Table 1. Data collection and handling. Bi 4g 0.3287(1) 0.1677(1) 0 0.0177(3) Ga(1) 4e 0.313(9) 1⁄2 1⁄2 0.2606(6) 0.0228(12) Al(1) 4e 0.687 1⁄2 1⁄2 0.2606 0.0228 Ga(2) 4h 0.499(7) 0.1490(3) 0.3377(4) 1⁄2 0.0164(10) Al(2) 4h 0.501 0.1490 0.3377 1⁄2 0.0164 O(1) 4g 0.356(1) 0.423(1) 0 0.0127(4) O(2) 4h 0.366(1) 0.409(1) 1⁄2 0.0114(3) O(3) 8i 0.130(1) 0.206(1) 0.251(1) 0.0254(3) O(4) 2d 0 1⁄2 1⁄2 0.0215(5) Table 2. Atomic coordinates and displacement parameters (in A). Atom Site Occ. x y z Uiso