Developments in Ceramic Materials Research

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126 José M. Rojo, José L. Mesa and Teófilo Rojo Therefore, a three-dimensional (3D) antiferromagnetic coupling is formed by ferromagnetic layers in the (100) plane disposed antiparallel between them. This overall antiferromagnetic arrangement is ordered with superexchange interactions between moments of one chromium atom with its six nearest neighbors via (PO4) tetrahedra. The magnetic ordering is similar to that obtained for Mo(PO3)3. However, the magnetic moments in the Cr metaphosphate are ferromagnetically ordered along the z direction in the (010) plane with an angle of 13° over the x axis (see Figure 22) whereas in the Mo phase the magnetic moments are along the x axis. This different ordering is probably the origin of the small differences observed in the magnetic behavior, where a good fit to a Heisenberg simple cubic antiferromagnetic system (S= 3/2) in the Cr(PO3)3 phase was not possible. The magnetic structure of Fe(PO3)3 is qualitatively different with ferromagnetic arrangements along the x and y directions and antiferromagnetic couplings along the z axis. The thermal evolution of the D1B neutron diffraction patterns from 1.8 to 8.5 K for Cr(PO3)3 is shown in Figure 23(a). The extra magnetic peaks, which are caused by the antiferromagnetic long-range magnetic ordering in the sample, appear below 5 K. The lower 3D magnetic ordering temperature with respect to the Fe(PO3)3 metaphosphate (TN≅ 9 K) could be attributed to the higher spin number in Fe(III) (S= 5/2) than in Cr(III) (S= 3/2). The intensity of the magnetic reflections increases without reaching a maximum at 1.8 K probably due to the low temperature at which the three-dimensional antiferromagnetic ordering appears. The thermal variation of the refined magnetic moments is shown in Figure 23(b). The Mx refined magnetic components are always higher than those of the Mz components and both curves seem to indicate the presence of a first contribution of the Mx moment near the ordering temperature. Figure 23 (Continued). a
Synthesis, Spectroscopic and Magnetic Studies… 127 Figure 23. Thermal evolution of (a) the neutron diffraction patterns of Cr(PO 3) 3 and (b) the ordered magnetic moments [M, Mx and Mz] in Cr(PO3) 3. b The thermal dependence of the ordered magnetic moments is different from that observed in the Fe(PO3)3 phase where the overall magnetic moment M, over the whole range of temperatures studied, is always lower than the Mx refined magnetic component although in both phases the x direction is the main direction to propagate the exchange interactions via (PO4) tetraedra. In this way, the presence of three different sites for the metallic ions in the structure is not relevant enough to give rise to local reorientations of the ordered moments and a weak ferromagnetic component is not observed in M(PO3)3 (M= Cr, Mo). In the Fe(PO3)3 phase, the competition of the magnetic interactions due to the higher spin number in Fe(III) (S= 5/2) than in Cr(III) (S= 3/2) and its magnetically isotropic behavior, together with the possible frustration between ions in the (100) layers, and the electronic configuration (d 5 ), are probably responsible for the presence of a weak ferromagnetic component as observed from magnetization measurements. 7.1.2. B-Type Cr(PO3)3 The magnetic peaks for Cr2(P6O18) observed at 1.8 K in the D2B neutron diffraction data were indexing using the nuclear cell. In the crystal structure, the magnetic atoms occupy one crystallographic site in a 4e general position of P21/a space group, numbered, 1a, 1b, 1c and 1d. The best agreement between the observed and calculated diffraction patterns (see Figure 24) is obtained when the magnetic moments lie in the (100) plane (Mx = 0). The refined magnetic components are My = 1.6(2) μB and Mz = 1.63(7) μB, with a resultant magnetic moment of 2.3(1) μB per Cr(III) ion. In the final refinement, the nuclear and magnetic discrepancy factors of Cr2(P6O18) are Rp = 6.37, Rwp = 9.05, χ 2 = 3.92, RBragg = 10.7 and Rmag = 12.5. The value of 2.3(1) μB at 1.8 K is lower than that of the experimental Cr(III) ion (3.09
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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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62 I, % 100 80 60 40 20 0 T. T. Bas
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68 Fluorescence, a.u. 1 T. T. Basie
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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Page 113 and 114: Synthesis, Spectroscopic and Magnet
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Page 179 and 180: D50 0.8 0.7 0.6 0.5 0.4 0.3 The Use
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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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