Developments in Ceramic Materials Research

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102 José M. Rojo, José L. Mesa and Teófilo Rojo Table 1. Selected IR bands (cm -1 ) and empirical assignments for the M(PO3)3 (M III = Ti, V, Cr, Mo and Fe) metaphosphates between 400 and 1500 cm -1 vs, very strong; s, strong; m, medium; w, weak. Table 2. Diffuse reflectance data of M(PO3)3 (M III = Cr 1, Mo 3 and Cr2(P6O18) 2 C r 1 Mo 3 Cr 2 E (cm -1 ) E/B E (cm -1 ) E/B E (cm -1 ) E /B 4 A 2g 4 T 2g(F) 16000 22.1 23000 50.3 15800 25.5 4 A 2g 4 T 1g(F) 22500 34.6 28100 61.5 22000 35.5 4 A 2g 2 E g 14700 20.3 10200 22.3 14600 23.5 4 A 2g 2 T 1g 15400 21.3 10600 23.2 15300 24.5 4A 2g 2 T 2g 21300 29.4 16000 35.0 21800 35.0 Dq (cm -1 ) 1600 2300 1580 B (cm -1 ) 650 457 620 C (cm -1 ) 3390 2180 3412 % reduction 71 75 68
Synthesis, Spectroscopic and Magnetic Studies… 103 The diffuse reflectance spectrum of Ti(PO3)3 exhibits a strong band centered at 17300 cm -1 which corresponds to the spin allowed transition 2 Eg � 2 T2g in an octahedral symmetry and can be associated with the ligand-field splitting parameter 10 Dq. A shoulder can be observed at 14800 cm -1 which is attributed to the Jahn-Teller splitting of the excited 2 Eg state. The diffuse reflectance spectrum of V(PO3)3 shows two absorptions centered at 24400 and 33600, which are assigned to the spin allowed transitions 3 T1g(F) � 3 T2g(F) and 3 T1g(P), respectively. Moreover, there is a weak signal about 10200 cm -1 which corresponds to the spin forbidden transition 3 T1g(F) � 1 Eg, 1 T2g. Using a simple crystal field approximate model for an octahedral d 2 system the Dq and Rach (B and C) parameters were calculated as Dq= 1610 cm -1 , B= 665 cm -1 and C= 1863 cm -1 .The values obtained are in good agreement with those given in the literate for this kind of compounds [23-25]. For chromium compounds, Cr(PO3)3 (1) and Cr2(P6O18) (2), two strong absorptions were observed at 16000, 22500 and 15800, 22000 cm -1 for (1) and (2), respectively. The bands corresponding to the Mo(PO3)3 (3) were observed at 23000 and 28100 cm -1 . These results are in good agreement with those observed for the Cr(III) and Mo(III) in octahedral geometry [23,26-29]. Using a simple crystal field approximate model, the ligand-field splitting parameter 10 Dq and the Racah parameter B may be calculated from the energies of the two lowest spin allowed transitions. For (1) we are find Dq= 1600 cm -1 and B= 690 cm -1 and for (3) Dq= 2300 cm -1 and B= 475 cm -1 . The values obtained for compound (2) are 1580 and 620 cm -1 for the Dq and B parameters, respectively. The B values for (1)-(3) are approximately 70% of those corresponding to the free ions (918 and 610 cm -1 for the chromium and molybdenum, respectively). This fact implies a significant degree of covalence in the M-O-M (M= Cr and Mo) bonds. The weak absorptions observed at 14700, 15400 and 14600, 15300 for (1) and (2), respectively and 10200 and 10600 for phase (3) may be assigned to the spin forbidden transitions 4 A2g � 2 Eg 2 T1g considering the ratios Dq/B of 2.46 and 2.55 and 5.03 for the chromium and molybdenum compounds. The signals of lower energy can be attributed to the transition 4 A2g � 2 Eg given in the diagram levels of Figure 2. The values of the C parameters obtained from the forbidden transition are 3390, 3412 and 2180 cm -1 , respectively. Finally, the weak absorptions observed at 21300, 21800 and 16000 cm -1 for compounds (1), (2) and (3), respectively, may be assigned to the spin forbidden transition 4 A2g � 2 T2g. In the case of the molybdenum metaphosphate this band appears at lower frequency than that observed for the spin-allowed transition 4 A2g � 2 T2g(F) as expected following the energy levels of these compounds (Figure 2). The diffuse reflectance data show that both allowed and forbidden transitions have higher E/B ratios in the molybdenum metaphosphate than in the chromium phases. This fact is due to the different positions of these metallic ions in the transition series (Table 2). Besides, the value of the Racah parameter B is higher in the chromium compounds than in the molybdenum phase, but the percentage of reduction of the B parameter ( ≅ 70%) is indicative of a similar degree of covalence in the M-O (M= Cr, Mo) bonds, in these compounds. In the diffuse reflectance spectrum of Fe(PO3)3 very weak characteristic bands belonging to Fe 3+ are present. These bands correspond to the forbidden transitions of a d 5 high spin configuration cation from the ground level 6 A1g( 6 S) to the excited 4 T1g( 4 G) , 4 T2g( 4 G) , 4 A1g( 4 G), 4 Eg( 4 G) and 4 T2g( 4 D) levels. The low intensity of the bands makes difficult the assignation of their maxima and, so, to calculate both the Dq and Racah (B and C) parameters.
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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22 Leslie G. Cecil Table 3. Mahalan
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24 Leslie G. Cecil Ixlú and Ch’i
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26 Leslie G. Cecil structures (D. R
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28 Leslie G. Cecil paste and Macanc
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30 Leslie G. Cecil Bieber, A. M. Jr
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32 Leslie G. Cecil Kepecs, S. M., a
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34 Leslie G. Cecil Schele, L., Grub
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36 Z. C. Li, Z. J. Pei and C. Tread
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The Use of Ceramic Pots in Old Wors
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IACC ( τ ) = t2 ∫ The Use of Cer
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where σ res is the scattering cros
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D50 0.8 0.7 0.6 0.5 0.4 0.3 The Use
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Definition (D50) 1 0.95 0.9 0.85 0.
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212 R. Ramesh, H. Kara, Ron Stevens
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220 ε S 33 R. Ramesh, H. Kara, Ron
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242 Development of Display Technolo
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244 Li Chen technology moved to the
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246 Li Chen The continuing evolutio
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248 Li Chen the back contact cathod
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250 Li Chen Figure 3. Vertical side
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252 Li Chen Figure 6. Molybdenum mi
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254 Li Chen Figure 8(a). I-V curve
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256 Li Chen Figure 9. Life time tes
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258 Figure 11(a). Plasma generated
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260 Li Chen [13] C.A. Spindt, K.R.
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262 S. Ardizzone, C. L. Bianchi, G.
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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