Forms of iron occurrence in a series of binary tellurides FexTi1−x Te1.45

Abstract

Nonstoichiometric tellurides Fe x Ti 13x Te 1.45 synthesized at 850oC were studied by X-ray phase and X-ray fluorescence analysis and by 57 Fe M1 ossbauer spectroscopy. The mutual iron3titanium substitution is limited in this series. The system contains four individual phases in which iron is in three different states: Fe 2+ in an asymmetric environment, Fe 2+ in a symmetric environment, and Fe 0 . The distribution of various iron states in the system depends not only on the Fe : Ti ratio, but also on the structure of phases.Nonstoichiometric compounds corresponding to the formula M 3 Ch 4 are formed in almost all binary systems transition metal (M)3chalcogen (Ch). Depending on the metal and chalcogen, the M 3 Ch 4 homogeneity areas can be different, and the structures of the forming chalcogenides are conventionally considered as intermediate between nickeline and cadmium iodide, NiAs6CdI 2 [1].Previously we have studied the formation of phases in binary systems Ti3Te [2] and Fe3Te [3] on a section from mono-to ditelluride. It was found that a series of nonstoichiometric tellurides MTe y belonging to the homogeneity area of M 3 Ch 4 exist in both binary systems. The choice of the index at tellurium y = 1.45, i.e., of the composition Fe x Ti 13x Te 1.45 as the subject of this study, was governed by the existence of the corresponding binary phases as extreme members in each system with the minimal value of parameter c for hexagonal titanium tellurides, by a common mode of tellurium hexagonal packing, and also by the hexagonal structure of TiTe 1.45 and FeTe 1.45 , which is intermediate between the structure of nickeline and cadmium iodide (NiAs6CdI 2 ). These facts allow us to expect that solid solutions will be formed in the system under consideration, at least in a restricted composition area. At the same time, the width of the homogeneity area of a solid solution strongly depends on the radii of atoms substituting each other. Therefore, determination of the states of metals in these phases becomes important.Polycrystalline samples of the composition Fe x . Ti 13x Te 1.45 (x = 0, 0.1, 0.2, ..., 1.0) were synthesized by the direct ampule technique. The starting substances were tellurium (ultrapure grade, T3A 1 class), iron produced from carbonyl (ultrapure grade, 6-2 class), and titanium obtained from titanium hydride by dehydrogenation in a vacuum at 850oC (according to atomic emission spectral analysis, it contained the following impurities, wt %: Fe 0.03, Si 0.01, Al 0.01, and Cr 0.001). To avoid oxidation, the metals were stored in evacuated ampules. The stoichiometric amounts of the starting substances were placed in vacuum-compression quartz ampules, which were evacuated to a residual pressure of 0.13 Pa and sealed. The synthesis was carried out in a muffle with stepwise heating: samples were calcined at 550oC for 125 h for the primary reaction, then at 750oC for 120 h, and finally at 850oC for 90 h with the subsequent quenching at 0oC. Each composition was duplicated.The composition of the synthesized produ...

Atomic spectrometry update—X-ray fluorescence spectrometry

“…Xray fluorescence was used, mainly in combination with XRD, to characterise the following new crystalline materials: TlInS 2 crystals, 213 La 0.8 Sr 0.2 MnO 3 powder, 214 PbMoO 4 crystals, 215 polyoxomolybdate-lanthanide complexes, 216 LaMgAl 11 O 19 crystals, 217 MgB 2 superconductor, 218 Ba 1Àx Sr x TiO 3 powders, 219 Fe x Ti 1Àx Tel. 45 tellurides, 220 Bi 2 O 3 doped ZnO ceramic varistors, 221 a ZrPO 4 fluoride, 222 and BaTiO 3 powders. 223 9.3 Environmental 9.3.1 Atmospheric particulate matter.…”