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Nanocrystalline iron-rich intermetallic compounds Sm2Fe17−xSix ( x = 0 , 1 , 1.5 , 2 ) were studied by means of X-ray diffraction coupled with magnetic and magnetocaloric properties measurements. The mechanically alloyed and annealed compounds were single phase and crystallize into the R 3 ¯ m Th2Zn 17 -type structure. The favorable ratios of the X-ray atomic factor f Si / f Fe allowed the location of the Si atoms in the R 3 ¯ m structure. The best Rietveld agreement factor assessed for a preferential occupation of Si on the 18h site. The Curie temperature was found to increase with Si content x from 436 K for x = 0 up to 525 K for x = 2, whereas the unit-cell parameters, measured with a standard element, were found to decrease with Si content. The random magnetic anisotropy model was used to determine the random anisotropy fields and the local random anisotropy constant. These nanocrystalline Sm2Fe17−xSix systems gave good magnetocaloric properties, which however decreased with Si content from 3.29 J/kg K for x = 0 down to 2.54 J/kg K for x = 2, at low field μ 0 H = 1.57 T. [ABSTRACT FROM AUTHOR]

To substitute NdFeB in many fields, the 1–12 phase is actively studied. That's the reason why magnetic and magnetocaloric properties of ThMn 12 have been investigated. NdFe 11 Ti and SmFe 10 V 2 were synthesized form bulk materials by arc melting and reduced into a powder by high energy ball milling to obtained a nanometric powder. Then, the powder was annealed in a furnace at different temperatures to crystallize the phase. Rietveld refinement showed that these two alloys crystallized in a ThMn 12 tetragonal structure which can be described by the I4/mmm space group. We found T C = 552 K , μ 0 H C = 1.2 × 10 - 2 T , R C P = 42 J.kg - 1 for NdFe 11 Ti and T C = 603 K , μ 0 H C = 0.4 T , R C P = 46 J.kg - 1 for SmFe 10 V 2 . It can be assumed that SmFe 10 V 2 is a hard magnet but not NdFe 11 Ti , both could be used as heat-pump. [ABSTRACT FROM AUTHOR]

In this work, we investigated the temperature dependence of short and long-range ferroelectric ordering in Pb0.55La0.30TiO3 relaxor composition. High-resolution x-ray powder diffraction measurements revealed a clear spontaneous macroscopic cubic-to-tetragonal phase transition in the PLT relaxor sample at ∼60 K below the maximum of the dielectric constant peak (Tm). Indeed, the x-ray diffraction (XRD) data showed that at 300 K (above Tm but below the Burns temperature, TB) the long-range order structure corresponds to a macroscopic cubic symmetry, space group number 221 (Pm-3m), whereas the data collected at 20 K revealed a macroscopic tetragonal symmetry, space group number 99 (P4mm) with c/a=1.0078, that is comparable to that of a normal ferroelectric. These results show that for samples with tetragonal composition, the long-range ferroelectric order may be recovered spontaneously at cryogenics temperatures, in contrast to ferroelectric samples with rhombohedral symmetry. On the other hand, x-ray absorption spectroscopy investigations intriguingly revealed the existence of local tetragonal disorder around Ti atoms for temperatures far below Tm and above TB, for which the sample presents macroscopic tetragonal and cubic symmetries, respectively. [ABSTRACT FROM AUTHOR]

The local structure of monoclinic, monohydrate, hexagonal, and pyrochlore WO3 phases was investigated by the extended x-ray absorption fine structure spectroscopy as preliminary studies of model compounds of amorphous and thin film WO3 based electrochromic species. In the four cases, we found a large W–O distribution of distances ranging from 1.70 to 2.35 Å. The apparent discrepancy of these results and previously published crystal structures are discussed and interpreted as the detection of vacancies and local distortion disorder. [ABSTRACT FROM AUTHOR]

Several x-ray powder diffraction measurements are conducted to analyze the spontaneous long and short-range ferroelectric ordering observed in the [Pb.sub.0.55][La.sub.0.30]Ti[O.sub.3] ceramics. The different characteristics of the ferroelectric order observed in different shaped ceramics are also analyzed.