Developments in Ceramic Materials Research

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112 José M. Rojo, José L. Mesa and Teófilo Rojo with Cm= 0.86 cm 3 Kmol -1 and θ= -7.2 K. The negative temperature intercept together with the observed decrease in the effective magnetic moment with decreasing temperature (Figure 10) suggests the presence of antiferromagnetic interactions in this compound. Figure 9. Thermal evolution of the χ m -1 and χmT product of Ti(PO 3) 3. Figure 10. Thermal evolution of the χ m -1 and χmT product of V(PO 3) 3. Dotted and continuous lines represent the best fit considering only the effect of the zero-field splitting and the J exchange parameters, respectively.
Synthesis, Spectroscopic and Magnetic Studies… 113 However, it is necessary take into occount that similar behavior could be also originate by a contribution such as a positive zero-field splitting, which was observed from the ESR data. Both contributions are qualitatively similar and to consider them simultaneously presents great difficulties. For this reason, we have tried to fit the experimental data under each of these hypothesis separately. Using the Van Vleck equation an analytical expression for the magnetic susceptibility as a function of the temperature and the D parameter was calculated [45]. However, considering the D value obtained from the Weiss temperature (θ= 2/3D), the calculated curve deviates drastically from the experimental ones (dotted line in Figure 10). Satisfactory fits can be obtained only by using D values higher than 40 K. However, these results are completely unrealistic considering the ESR measurements. An expression for the magnetic susceptibility was derived from high temperature expansion series for an antiferromagnetic Heisenberg simple cubic lattice calculated by Rushbrooke and Wood [46]. The best fit corresponds to the continuous line in Figure 10 and was obtained with a J/k value of -0.92 K. The calculated curve agrees rather well with the experimental one at high temperatures, but deviates appreciably at low temperatures where the effect of the zero-field splitting is more important. So, we can conclude that both the antiferromagnetic interactions and the zero-field splitting determine the magnetic behavior observed for V(PO3)3. 6.3. Magnetic Properties of M(PO3)3 (M= Mo and Cr) and Cr2(P6O18) The thermal evolution of the molar magnetic susceptibility for Mo(PO3)3 is shown in Figure 11. A sharp maximum is observed at 4.5 K, indicating the existence of an antiferromagnetic ordering in this compound. The high temperature data (T> 50 K) are well described by a Curie-Weiss law [χ=Cm/(T-θ)] with Cm= 1.71 cm 3 Kmol -1 and θ= -6.8 K. The negative temperature intercept together with the decrease of the effective magnetic moment observed when the temperature is lowered (3.64μB at 300 K and 1.78μB at 2 K) are in good agreement with the predominance of antiferromagnetic interactions in this compound (Figure 11). Considering the structural features of the molybdenum metaphosphate only superexchange interactions via (PO4) tetrahedra can be expected. Due to the complexity of three-dimensional arrangement and the consequent presence of different exchange pathways it is not possible to find a simple magnetic model, representing exactly the characteristics of the magnetic ordering in this compound. However, taking into account the weakness of the exchange couplings and the packing of the (MoO6) octahedra, a simple cubic network can be utilized in order to obtain an approximate value of the exchange parameter. Considering the usual isotropic magnetic behavior of Mo(III) ions a Heisenberg Hamiltonian was the starting point, H = 2J Σ SiSj, with i
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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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54 T. T. Basiev, V. A. Demidenko, K
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Page 113 and 114: Synthesis, Spectroscopic and Magnet
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The Use of Ceramic Pots in Old Wors
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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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Modeling of Thermal Transport in Ce
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q x = Modeling of Thermal Transport
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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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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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