Crystal growth, structure determination and magnetism of a new hexagonal rhodate: Ba9Rh8O24

Abstract

During recent years, there has been much interest in the preparation and investigation of oxides structurally related to the 2H hexagonal perovskites, the prototype of which, Sr 4 PtO 6 , was first prepared by Randall and Katz 1 and forms in the K 4 CdCl 6 structure type. As shown by Darriet and Subramanian, 2 and more recently by Darriet and Perez-Mato, 3 the structures of these oxides can all be described as resulting from stacking sequences of m[A 3 O 9 ] layers and n[A 3 AAO 6 ] layers, with the subsequent filling of the interstitial octahedral sites. The general formula that can be derived from the stacking of such layers is: A 3n + 3m AA n B 3m + n O 9m + 6n (n, m = integers, A = alkaline earth; AA, B = large assortment of metals including alkali, alkaline earth, transition, main group, and rare earth metals). The structures are characterized by one-dimensional chains of face-sharing trigonal prisms and octahedra along the c-axis of the hexagonal unit cell.Sr 4 PtO 6 is the n = 1, m = 0 member of this family and consists of chains of alternating face-sharing octahedra and trigonal prisms. While many n = 1, m = 0 members are known, for example Sr 3 NaRhO 6 , 4 Ca 3 Co 2 O 6 , 5,6 and Ca 3 CuIrO 6 , 7 far fewer oxides with higher integer values of n and m have been prepared and structurally characterized. In addition, until recently, most structure determinations were based on Rietveld refinements of polycrystalline powders and few single crystals of any members, and in particular very few members with higher integer values of n and m, have been grown and structurally characterized. A recent example of the latter type includes Ba 8 CoRh 6 O 21 corresponding to the m = 5, n = 3 member. 8 Other examples include Ba 6 Ni 5 O 15 , 9 Sr 4 Ru 2 O 9 , 10 and the incommensurate phases of Ba 1 + x (Cu x Rh 1 2 x )O 3 (x = 0.1605 and 0.1695) whose average structure is that of the n = 3, m = 4 member with a repeat sequence of five octahedra and one trigonal prism. 11 In this communication we report the first structural characterization of the m = 2, n = 1 member Ba 9 Rh 8 O 24 and the investigation of its magnetic properties.Single crystals of Ba 9 Rh 8 O 24 were grown from a molten potassium carbonate flux. BaCO 3 and Rh metal powder (6:1 molar ratio) were mixed with a 10 fold mass excess of K 2 CO 3 . The alumina crucible was heated in air to 1050 °C, held for 48 h, and then quickly cooled to room temperature. The crystals were isolated manually by dissolving the flux in water.An approximate [110] view is shown in Fig. 1. The structure is characterized by infinite chains containing groups of seven face-sharing RhO 6 octahedra separated by one face-sharing RhO 6 trigonal prism. These chains are in turn separated from one another by chains of Ba cations. The metal-oxygen bond distances [Rh1-O1 2.020(6), Rh2-O2 2.008(6), Rh2-O1 2.035(6), Rh3-O3 2.003(7), Rh3-O2 2.035(6), Rh4-O4 1.969(10), Rh4-O3 2.048(7), Rh5-O4 2.012(12) Å] are typical for oxides of this type. Intrachain Rh-Rh bond distances [Rh1-Rh2 2.523(1), Rh2-Rh3 ...

Ba3MxTi3−xO9(M=Ir

“…However, no further detailed information on the crystal structure of Ba 3 RhTi 2 O 9 was provided. Our laboratory x-ray diffraction pattern (not shown) of the nominal Ba 3 RhTi 2 O 9 has shown the extra lines as well, which were identified as coming from Ba 9 Rh 8 O 24 impurity [27]. Even with this impurity introduced into the refinement, there are still a few spurious lines in the pattern, due to low amounts of other impurities.…”

“…The refined crystal structure parameters at room temperature are given in Table II. The second compound, with a target nominal composition Ba 3 Rh 0.5 Ti 2.5 O 9 , did show a much smaller amount (<1.5%) of Ba 9 Rh 8 O 24 impurity [27], and the refined composition is Ba 3 Rh 0.432(18) Ti 2.568(18) O 9 . The Rietveld refined pattern is shown in Fig.…”

Crystal growth, structure determination and magnetism of a new m=3, n=1 member of the A3n+3mA′nB3m+nO9m+6n family of oxides: 12R-Ba12Rh9.25Ir1.75O33

“…In addition, an ever increasing number of examples of other structures, including Sr 6 Rh 5 O 15 (n ¼ 1; m ¼ 1) [23,24], Ba 8 CoRh 6 O 21 (n ¼ 3; m ¼ 5) [25], Ba 9 Rh 8 O 24 (n ¼ 1; m ¼ 2) [26], Sr 4 CuIr 2 O 9 (n ¼ 3; m ¼ 1) [27], and Ba 5 PdMn 3 O 12 (n ¼ 3; m ¼ 2) [28] have been prepared as both powders and in single-crystal form.…”

Crystal growth of new strontium iron rhodium oxides: Sr4Fe0.73Rh2.27O9 and SrFe0.71Rh0.29O3

“…Several research groups have succeeded in growing single crystals of oxides belonging to this family from molten alkali carbonates [6][7][8], while other fluxes, such as hydroxides or chlorides, have been used with almost equal success [9][10][11][12]. Research within our group has focused on the systematic preparation of single crystals via high temperature flux growth using hydroxide and carbonate melts [1,6,[13][14][15][16][17][18][19].…”