J. MATER. CHEM., 1991, 1(6), 1027-1029 New Antimonate-Vanadate with the Rutile Structure Josefa Isasi, Maria Luisa Veiga, Antonio Jerez, Maria Luisa Lopez and Carlos Pico* Departamento de Quimica Inorganica I, Universidad Complutense, Facultad de Ciencias Quimicas, 28040 Madrid, Spain VCrSbO, has been prepared and its magnetic and electronic properties investigated. The crystal structure was refined from X-ray powder diffraction by the Rietveld method. The unit cell is tetragonal (space group P4,/rnnm, Z=2),a=4.5708(4) A and c=3.0281(3) A. The compound is isostructural with the rutile phase FeNbO, and stoichiometric with respect to all three constituent metals atoms. The electron diffraction pattern is consistent with a tetragonal symmetry. Keywords: Rutile; Antirnonate ; Vanadate The ideal rutile structure may be described as an idealized hexagonal close-packed oxygen lattice with octahedrally co- ordinated metal ions forming edge-shared infinite chains along the [OOl] direction of the tetragonal unit cell (P4,lmnm).These chains are cross-linked by octahedra sharing corners to form an equal number of identical vacant channels. Cation- cation interactions often occur between metal ions in the c direction, with edge-sharing octahedra, resulting in anomal- ously short metal-metal distances, and/or some structural modifications of the rutile type' can occur. Previous work concerning vanadium and niobium mixed oxides with genera! formula M02 (CrVNbO,, FeVNb06, NiV2Nb2010, Cr2V2WOlo and Cr2Nb2WOlo)2-5 has been reported.It was shown that these compounds adopt the ideal rutile structure and form grossly non-stoichiometric phases with retention of this structure. The semiconducting, electronic and magnetic properties may be correlated with the number of unpaired d electrons introduced into the rutile network. In addition to these interesting properties, some of these oxides have been investigated for potential application in the photoelectrolysis of water6-and as possible cathode materials for high-energy- density secondary batteries." In the course of our research of the chemical and structural relationships between SbV oxocompounds and those of NbV and Tav congeners, this paper describes the synthesis, crystal structure, electronic and magnetic properties of the rutile phase VCrSbO6.Experimental VCrSb06 was prepared by heating a mixture (in evacuated silica glass tubes) of Cr203 (Merck), V,04 (Merck) and Sb205 synthesized in the stoichiometric ratio, at 1163 K for 24 h. The absence of impurity phases was established from electron diffraction patterns. Powder X-ray diffraction patterns were registered at rate of 0.1" (28) min-' by means of a Siemens D500 diffractometer powered by a Kristalloflex generator using Ni-filtered Cu-Ka radiation. A 28 step scan of 0.04" was used, and Rietveld's profile analysis method" was employed for refinement of X-ray diffraction results in the 20 range 10- 120" for observed reflections. Electron diffraction was performed with the electron micro- scope JEOL 2000 FX operating at 200 kV.The sample was crushed and dispersed in acetone. The magnetic susceptibility measurements were made in the temperature range 4.2-300K, using a DSM-5 pendule magnetometer. The maximum magnetic field was 14 kG with HdH/dz =29 kG2 cm -'. The set-up was calibrated with Hg[Co(SCN),] and Gd2(S04)3 and was independent of the magnetic field in the temperature range used in these experiments. For the electrical resistivity measurements, the pelletized sample was sintered at 1163 K for 24 h. The electrical resis- tivity was measured using the van der Pauw', method. Contacts were made via silver paint on the sample discs; their ohmic behaviour was established by measuring their current- voltage characteristics. Results and Discussion X-Ray diffraction results were analysed by means of the Rietveld method.The program used minimises the function x2 =(R,p/REXp)2 and the best reliability factors were calcu- lated for a rutile-like model: Rp=100 1[Yi-Yci]/C [Yi]=18.3 1 I Rw,=100 {C [Wi (Yi-YCi)2]/C[wiY2])1/2=22.5 1 I Rg=100 1[Zi-I,-i]/E [Zj]=8.08 I I -(1ci)''2]/1RF= 100 [(Ii)1/2 (Ii)l',=8.83 I I The reflection conditions: k+1=2n (for Okl) I=2n (001) and h=2n (hOO) are compatible with the space group P4,/ mum. The unit-cell parameters were refined to the values a= 4.5708(4) 8, and c=3.0281(3) A. The atomic coordinates and bond lengths for VCrSbO, are presented in Table 1. The good agreement between the observed and calculated diffraction profiles appears in Fig.1. Fig. 2 shows the rutile structure in which Cr, Sb, and V octahedra are statistically distributed, forming edge-shared infinite chains along the [00 1) direction of the tetragonal unit cell. These chains are cross-linked by other octahedra sharing corners. The metal-oxygen distances are in agreement with the sums of the ionic radii as given by Shannon.I3 Fig. 3 shows the electron diffraction pattern along zone axis [1 111, consistent with tetragonal symmetry. Mag- netic measurements were performed at 4.2-300 K and show that the magnetic behaviour us. temperature for VCrSbO, is dependent only on the crystal structure and the oxidation Table 1 Atomic coordinates and bond lengths for CrVSbO, atom site Cr, V, Sb 2a 0 4f M-0 = 1.892 A x 2 M-0=2.021 Ax4 X Y Z 0 0 0 0.2928(3) 0.2928(3) 0 Fig.1 The observed (dots), calculated (full line) and difference diffrac- tion profiles for VCrSbO, Fig. 2 The rutile structure: CrO,, VO, and SbO, octahedra statisti- cally distributed forming edge-shared infinite chains along the [OOI] direction J. MATER. CHEM., 1991, VOL. 1 states of the cations involved in the compound. The magnetic susceptibility follows a Curie-Weiss law above 180 K, and no maximum in the curve has been found in the temperature range 4.2-300K CFig.41. This effect showed that the metal ions do not have antiferromagnetic ordering (ie.the paramag- netic ions are randomly distributed and hence also are the antimony ones) and the sample showed paramagnetic behav- iour.The Curie constant was 2.1 1, which is consistent with that expected from the contributions of V4+ (s= l/2) and Cr3+ (s=3/2); the Weiss constant was 8= -24.01 K. The electrical conductivity us. l/T, was studied for CrVSbO, (Fig. 5). From the results, one can deduce that this oxide is a classical semiconductor according to the law CJ=CI~ exp(-AE/k,T). This compound has a conductivity at 01 1 1 I I 1 0 60 120 I80 240 300 TI Fig. 4 Temperature dependence of the molar susceptibility of VCrSbO, \ I I 2.0 3 .O 4.0 1O3KI7 Fig. 3 The electron diffraction pattern along the zone axis [1171 of VCrSbO, Fig. 5 In(Conductivity) us. 103/T J.MATER. CHEM., 1991, VOL. 1 1029 room temperature of a=2.16 x R-' cm-' with E,= 0.38 eV. The transport properties are a result of localization of the 3d3 electrons on the Cr3+ ions (and 4d" in Sb5+ ions) which are unlikely to participate in M-M bonding. Metallic interactions would therefore be limited and semiconducting 3 4 5 M. Greenblatt, K. R. Nair, W. H. McCarroll and J. V. Wszczak, Muter. Res. Bull., 1984, 19, 777. K. R. Nair, M. Greenblatt and W. H. McCarroll, Muter. Res. Bull., 1983, 18, 1257. K. R. Nair, M. Greenblatt and W. H. McCarroll, Muter. Res. Bull., 1981, 18, 305. behaviour would result in this compound. The disordered distribution of metal ions with different orbital energies is likely to be sufficient for semiconducting behaviour.6 7 B. Khazai, R. Kershaw, K. Dwight and A. Wold, J. Solid State Chem., 1981, 39, 395. B. Khazai, R. Kershaw, K. Dwight and A. Wold, J. Solid State Chem., 1981,39, 294. We thank F. Rojas for the magnetic measurements. This work 8 H. Leiva, K. Dwight and A. Wold, J. Solid State Chem., 1982, 41, 42. is supported by the CICYT (Spain). J.I. and M.L.L. are grateful to the UCM for the 'Beca complutense'. 9 10 P. H. M. de Korte and G. Blasse, J. Solid State Chem., 1982, 44, 150. D. W. Murphy, F. J. Disalvo, J. N. Carides and J. V. Waszcak, Muter. Res. Bull., 1978, 13, 1395. References 11 J. Rodriguez-Carvajal, Program Fullprof, ILL, Grenoble, France, 1990. 1 C. J. Chen, M. Greenblatt, K. Ravindran Nair and J. V. Waszczak, 12 L. J. Van der Pauw, Philips Res. Rep., 1958, 1, 13. 2 J. Solid State Chem., 1989, 81, 64. K. Ravindran Nair and M. Greenblatt, Muter. Res. Bull., 1982, 13 R. D. Shannon, Acta Crystallogr. Sect. A, 1976, 32, 751. 17, 1057. Paper 11026335; Received 3rd June, 1991