Investigations on Bi25FeO40 powders synthesized by hydrothermal and combustion-like processes

Abstract

The syntheses of phase−pure and stoichiometric iron sillenite (Bi 25 FeO 40) powders by a hydrothermal (at ambient pressure) and a combustion−like process are described. Phase−pure samples were obtained in the hydrothermal reaction at 100 °C (1), whereas the combustion−like process leads to pure Bi 25 FeO 40 after calcination at 750 °C for 2 h (2a). The activation energy of the crystallite growth process of hydrothermally synthesized Bi 25 FeO 40 was calculated as 48(9) kJ mol −1. The peritectic point was determined as 797(1) °C. The optical band gaps of the samples are between 2.70(7) eV and 2.81(6) eV. Temperature and field−depending magnetization measurements (5−300 K) show a paramagnetic behaviour 2 with a Curie constant of 55.66•10 −6 m 3 •K•mol −1 for sample 1 and C = 57.82•10 −6 m 3 •K•mol −1 for sample 2a resulting in magnetic moments of µ mag = 5.95(8) µ B •mol −1 and µ mag = 6.07(4) µ B •mol −1. The influence of amorphous iron−oxide as a result of non-stoichiometric Bi/Fe ratios in hydrothermal syntheses on the magnetic behaviour was additionally investigated.

Магнитные свойства порошков BiFe-=SUB=-0.93-=/SUB=-Mn-=SUB=-0.07-=/SUB=-O-=SUB=-3-=/SUB=-, полученных методом ультразвукового спрей-пиролиза

“…Наблюдаемое при комнатной температуре ферромаг-нитное поведение образцов отражает исключительно свойства основной фазы BiFe 0.93 Mn 0.07 O 3 , поскольку примесная фаза, следы которой обнаружены при рент-генофазовом анализе, не является ферромагнитной при комнатной температуре [23]. Отсутствие корреляции между магнитными свойствами и ОКР позволяет заклю-чить, что увеличение значений H c и M не связаны с уменьшением размеров нанокристаллов.…”

Electron diffraction study of the sillenites Bi12SiO20, Bi25FeO39 and Bi25InO39: Evidence of short-range ordering of oxygen-vacancies in the trivalent sillenites

“…11,12 The last decade has witnessed an increase in the study of these compounds for photocatalysis and novel applications. [13][14][15][16][17] The physical and electronic structure of sillenites remains important and continues to motivate synthesis, [18][19][20][21][22] optical, [23][24][25] first principles, [26][27][28] dielectric, 29 magnetism, 30 and high-pressure studies. 31,32 Figure 1 shows a representative sillenite structure.…”

“…19 This comprehensive model of sillenites is dependent on the conclusion by Radaev and Simonov that the parent γ -Bi 2 O 3 compound houses Bi 3+ in the center of the tetrahedron, 33,35,36 and that it is unlikely that Bi 5+ partially occupies the M site of divalent and trivalent sillenites. 19 Some recent publications instead claim a Bi 25 FeO 40 chemical formula for the iron sillenite, 17,22 and some justify the stoichiometry by citing work from Craig and Stephenson. 37 Unfortunately, some of the publications claiming the Bi 25 FeO 40 chemical formula 17,22,38 do not comment on the more recent, heavily cited, and comprehensive model of sillenites that uses Bi 3+ partial occupation of the M site.…”

“…19 Some recent publications instead claim a Bi 25 FeO 40 chemical formula for the iron sillenite, 17,22 and some justify the stoichiometry by citing work from Craig and Stephenson. 37 Unfortunately, some of the publications claiming the Bi 25 FeO 40 chemical formula 17,22,38 do not comment on the more recent, heavily cited, and comprehensive model of sillenites that uses Bi 3+ partial occupation of the M site. 19 The controversy is further complicated by the fact that some of the studies quoting the Bi 25 FeO 40 formula use the hydrothermal growth method.…”

“…19 The controversy is further complicated by the fact that some of the studies quoting the Bi 25 FeO 40 formula use the hydrothermal growth method. 22 In our study we used the solid-state growth method; therefore, we use the Bi 25 FeO 39 chemical formula due to the lack of experimental evidence for the stabilization of Bi 5+ in systems grown by the solid-state method.…”