JOURNAL OF SOLID STATE CHEMISTRY ARTICLE NO. 138, 347—349 (1998) SC987796 Mn0.15V0.3Mo0.7O3 , a New Compound in the MnV2O6 –MoO3 System Jacek Zió"kowski,1 Piotr Olszewski, and Bogna Napruszewska Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek, 30-239 Krako& w, Poland Received December 27, 1996; in revised form February 3, 1998; accepted February 10, 1998 In the past we studied the system MnV2O6 (monoclinic, C2/m, brannerite-type structure)–orthorhombic MoO3 , including the MnU 5 Mn12xUxV222x Mo2xO6 solid solutions (U 5 cation vacancy in the original Mn site, X 5 100x). MnU’s isomorphous with the MnV2O6 matrix appeared to be stable upto Xsat 5 42 at room temperature or atmost Xsat 5 45 at 520°C. Beyond these limits, MnUsat and o-MoO3 were observed to coexist. Now, a new phase Mn0.15V0.3Mo0.7O3 5 Mn0.3V0.6Mo1.4O6 (or almost, referred to as the Y phase) has been identified in the MnV2O6–MoO3 system at formal X 5 70. It is monoclinic P2/m (P2 or Pm) with a 5 11.829(2) As , b 5 3.657(1) As , c 5 10.330(2) As , b 5 101.54(1)°, and V 5 437.8(3) As 3. The Y phase prepared by a citrate precursor method starts to show reasonable (broadened) XRD reflections at 300°C, becomes predominant at 450°C, and decomposes slowly to MnUsat and o-MoO3 at higher temperatures (above 450°C). Apparently, due to the parallel course of the solid state reactions, an entirely pure Y phase has never been obtained. Samples with 654X 5 70 always contain some o-MoO3 traces whereas those with 70 5 X580 are contaminated with MnUsat . ( 1998 Academic Press 1. INTRODUCTION In our previous works (1—3) the defective brannerite-type phases have been described. Their monoclinic (most frequency C2/m) matrix is MeV O (Me"Mg, Mn, Co, Cu, 2 6 Zn). Isomorphous solid solutions are obtained on doping MeV O with orthorhombic MoO and/or monovalent 2 6 3 ¸ element oxides (¸"Li, Na, Ag, K (4)). The general formula of these solid solutions is Me¸'"Me '¸ 1~x~y x y V Mo O ('"cation vacancy in the original 2~2x~y 2x`y 6 Me/¸ site; X"100x and ½"100y). The particular case of these studies is the system MnV O —o-MoO , comprising the Mn'"Mn ' 2 6 3 1~x x V Mo O solid solutions stable up to Mn' of 2~2x 2x 6 4!5 X"42 at room temperature or at most up to X"45 at 520°C. Beyond these limits, the coexistence of Mn' and 4!5 o-MoO was observed (1). 3 On revising the MnV O —MoO system, we discovered 2 6 3 a new Y phase"Mn V Mo O "Mn V Mo 0.15 0.3 0.7 3 0.3 0.6 1.4 1 To whom correspondence should be addressed. O , formed at formal X"70 and stable in the limited range 6 of temperature 3004¹4450°C. The aim of this work is to characterize this new Y phase. 2. EXPERIMENTAL AND TREATMENT OF DATA The following samples, corresponding formally to the Mn' V Mo O system, have been considered/ 1~x 2~2x 2x 6 reconsidered: X"0, 10, 20, 30, 40, 42, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100 (series C"composition series). All samples were synthesized by the amorphous citrate method (5) adapted empirically to the present system (2). Reactants were MnCO , NH VO , (NH ) Mo O ) 4H O, 3 4 3 46 7 24 2 0.1 M ammonia, and citric acid, all of p.a. grade. The procedure has been described in ref 2. The final thermal treatment was carried in air at 520°C for 24—72 h, with grinding every 24 h; thereafter the samples were quenched. Discovery of the new Y phase induced us to study an additional series of samples (series T"temperature series) of composition X"70 but annealed at 300, 315, 325, 350, 400, 450, 500, 520, and 640°C for various times ranging from 24 to 200 h, with grinding every 24 h and pelleting in some cases. X-ray diffraction patterns were obtained with a DRON-2 diffractometer using CuKa radiation; in some cases, an Al internal standard (a"4.0492 As at 25°C) was used. Data were collected on a floppy disk and processed with the SMOK (6) program for deconvolution and analysis of the spectra. Reflections in the range 5°(2h(80° were used to determine the lattice constants. Further treatment of the data was performed with the following programs: PROSZKI (7) (involving, among others, DICVOL (8, 9), APPLEMAN (10), and LATCON (11)) and DBWS-9006 PC (12). DTA was performed with a SETARAM M5 microanalyzer (10°C/min, Pt crucibles, sample of about 12 mg, air atmosphere; treatment of DTA curves was described in ref 2). 3. RESULTS AND DISCUSSION First, dealing with C-series samples, we noticed that close to X"70, in addition to the reflections of Mn' and 4!5 347 0022-4596/98 $25.00 Copyright ( 1998 by Academic Press All rights of reproduction in any form reserved. 348 ZIÖ|KOWSKI, OLSZEWSKI, AND NAPRUSZEWSKA TABLE 1 Phase Composition of Samples in the MnV2O6 –MoO3 System Formally Corresponding to the Mn12xUxV222x Mo2xO6 Formula (X 5 100x) in the Temperature Range 300–520°Ca X TABLE 2 Powder Diffraction Data for Mn0.15V0.3Mo0.7O3 (Monoclinic, P2/m, a511.829(2) As , b53.657(1) As , c510.330(2) As , b 5 101.54(1)°; V 5 437.8(3) As 3 Phase compositionb k 04X442 42(X460 X"65 X"70 X"75 X"80 80(X(100 X"100 B B#Y Y#traces of B and minor traces of o-M Y#minor traces of B and o-M Y#traces of o-M and minor traces of B Y#traces of o-M and minor traces of B Y#o-M o-M a A very slow decomposition of Y is observed at 500 and 520°C; above 600°C the Y phase is melted and does not reappear on cooling. b B"brannerite (Mn' ) , Y"phase identified as Mn V Mo O , 4!5 0.15 0.3 0.7 3 o-M"orthorhombic MoO . 3 o-MoO , seven distinct reflections appear which cannot be 3 ascribed to any known phase. The unknown phase was preliminarily called the Y phase. A number of assays (Table 1) led us to the conclusion that the composition of the Y phase is most probably Mn V Mo O " 0.3 0.6 1.4 6 Mn V Mo O , although an entirely pure Y phase has 0.15 0.3 0.7 3 never been obtained (also in the T series). The aforementioned seven reflections were analyzed with PROSZKI (7). A reasonable solution was found only for the monoclinic P2/m (P2 or Pm) space group (no higher symmetry was found after further treatment of data). DICVOL gave about 20 solutions. Among them, we selected one satisfying the following requirements: high figure of merit (above 60); small volume of the unit cell (at most 500 As 3); the shortest unit cell parameter, at least 3.6 As , which corresponds to the smallest, credible diagonal of the MoO 3 octahedron, believed to be the smallest motive of the structure. The preliminary results (for seven reflections) smoothed by APPLEMAN and LATCON were about a"11.82 As , b"3.65 As , c"10.34 As , and b"101.3°. Further treatment consisted of calculating the reflection positions with DBWS (the latter program was used for an artificial phase to reach the entire list of 2h/hkl, and to increase the number of considered reflections), and searching for the best fit with PROSZKI. At the end, we selected 26 reflections sufficiently free of overlap or noise. They gave a"11.825(2) As , b" 3.654(1) As , c"10.328(2) As , and b"101.49(1)°. At 300°C the T-series samples began to show some broadened XRD reflections that could be ascribed to the Y phase and Mn' . At 400°C the first reflections of o4!5 MoO appeared. This means that in spite of the ‘‘citrate 3 mixing of reactants,’’ parallel solid state reactions take place. In the range 350—450°C the time of annealing and 1 !1 2 !2 !1 2 !2 !3 2 !1 1 !2 0 1 !4 3 !1 3 2 0 3 3 !5 5 6 !7 !4 !1 5 4 !1 !5 !2 !9 k l 2h 0"4 (deg) d 0"4 (As ) 2h #!-# (deg) d #!-# (As ) I/I 0 (%) 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 1 0 1 1 0 1 0 1 1 0 0 1 2 1 1 1 0 1 0 0 1 0 1 2 1 2 1 2 3 1 1 2 2 2 0 4 1 3 5 3 4 2 1 1 1 5 3 3 4 6 6 7 2 7.64 10.39 15.28 16.06 17.66 19.12 20.89 22.96 25.59 26.01 27.54 29.28 30.18 32.05 32.40 33.76 34.75 36.13 41.68 44.76 46.35 46.67 46.85 48.87 49.82 54.34 55.91 57.09 58.35 58.75 59.44 61.32 68.69 71.95 11.581 8.519 5.801 5.521 5.024 4.643 4.254 3.875 3.482 3.427 3.240 3.051 2.962 2.793 2.764 2.655 2.582 2.486 2.167 2.025 1.959 1.946 1.939 1.864 1.831 1.688 1.645 1.613 1.582 1.572 1.555 1.512 1.367 1.312 7.628 10.391 15.290 16.032 17.668 19.111 20.870 22.940 25.584 25.993 27.551 29.282 30.153 32.035 32.390 33.750 34.750 36.128 41.676 44.780 46.330 46.688 46.843 48.853 49.798 54.327 55.914 57.091 58.360 58.740 59.421 61.285 68.671 71.955 11.589 8.513 5.795 5.528 5.020 4.644 4.256 3.877 3.482 3.428 3.237 3.050 2.964 2.794 2.764 2.656 2.582 2.486 2.167 2.024 1.960 1.945 1.939 1.864 1.831 1.689 1.644 1.613 1.581 1.572 1.555 1.512 1.367 1.312 6 16 19 10 5 5 5 26 63 100 19 60 22 19 24 12 6 56 4 5 20 16 6 11 41 8 23 18 12 6 18 13 10 5 pelleting have no important influence on the XRD spectrum. At higher temperatures the Y phase slowly decomposes to Mn' and o-MoO . The Y phase never appeared 4!5 3 after melting at 640°C. The most pure Y phase was obtained at 450°C after 110 h of annealing. Treating the XRD spectrum with the same procedure as described earlier, we have come to the conclusions gathered in Table 2, based on 34 reflections. DTA of the sample treated at 450°C for 110 h showed a narrow endothermal doublet with an onset at 595°C, maxima at 607 and 615°C, and a sattelite ending at 682°C. Taking into account that the sample was not equilibrated, it seems significant that the onset and ending temperatures coincide well with the eutectic melting and liquidus in the MnV O —MoO system (1). 2 6 3 NEW COMPOUND Mn V Mo O 0.15 0.3 0.7 3 4. CONCLUSIONS MnV O (brannerite) and orthorhombic MoO form 2 6 3 a compound Mn V Mo O "Mn V Mo O , 0.15 0.3 0.7 3 0.3 0.6 1.4 6 appearing at 300°C and slowly decomposing above 450°C. The lattice constants of this monoclinic P2/m (P2 or Pm) compound are a"11.829(2) As , b"3.657(1) As , c" 10.330(2) As , b"101.54(1)°, and »"437.8(3) As 3. REFERENCES 1. R. Koz"owski, J. Zió"kowski, K. Moca"a, and J. Haber, J. Solid State Chem. 35, 1 (1980) (erratum, J. Solid State Chem. 38, 138 (1981)). 2. J. Zió"kowski, K. Krupa, and K. Moca"a, J. Solid State Chem. 48, 376 (1983). 349 3. B. Napruszewska, P. Olszewski, and J. Zió"kowski, J. Solid State Chem. 133, 545 (1997), and papers quoted therein. 4. P. Olszewski, B. Napruszewska, and J. Zió"kowski, J. Solid State Chem., in preparation. 5. P. Courty, H. Ajot, and C. Marcilly, Powder ¹echnol. 7, 21 (1973). 6. J. Wrzesiński, Elector Co., Kraków, Poland, 1992. 7. W. |asocha and K. Lewiński, J. Appl. Crystallogr. 27, 437 (1994). 8. D. Louer and M. Louer, J. Appl. Crystallogr. 5, 271 (1972). 9. D. Louer and R. Vargas, J. Appl. Crystallogr. 15, 582 (1982). 10. E. D. Appelman, H. T. Evans, and D. S. 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