Abstract:The preparation of a nano-sized LaFeO 3 powder by a soft-chemistry method using starch as complexing agent is described herein. Phase evolution and development of the specific surface area during the decomposition process of (LaFe)-gels were monitored up to 1000 °C. A phase-pure nano-sized LaFeO 3 powder with a high specific surface area of 25.7 m 2 /g and a crystallite size of 37 nm was obtained after calcining at 570 °C. TEM investigations reveal a porous powder with particles in the range of 20 to 60 nm. Ca… Show more
“…The average linear thermal expansion coefficients of Sm 0.5 Pr 0.5 FeO 3 and Sm 0.5 Nd 0.5 FeO 3 in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10 −6 K −1 . It is close to the TEC value of (10.8–11.8) × 10 −6 K −1 reported for LaFeO 3 [26, 27] and other rare earth ferrites confirming the suggestion that the nature of rare earth ions does not influence the thermal expansion in R FeO 3 [15]. Fig.…”
Mixed ferrites Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 with orthorhombic perovskite structure isotypic with GdFeO3 were synthesized by solid-state reaction technique in air at 1473 K. Structural parameters obtained at room temperature prove a formation of continuous solid solutions in the SmFeO3–PrFeO3 and SmFeO3–NdFeO3 pseudo-binary systems. Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 show strongly anisotropic nonlinear thermal expansion: thermal expansion in the b direction is twice lower than in the a and c directions. The average linear thermal expansion coefficients of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10−6 K−1, which is close to the values reported for the parent RFeO3 compounds. Subtle anomalies in the lattice expansion of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 detected at 650–750 K reflect magnetoelastic coupling at the magnetic ordering temperature TN.
“…The average linear thermal expansion coefficients of Sm 0.5 Pr 0.5 FeO 3 and Sm 0.5 Nd 0.5 FeO 3 in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10 −6 K −1 . It is close to the TEC value of (10.8–11.8) × 10 −6 K −1 reported for LaFeO 3 [26, 27] and other rare earth ferrites confirming the suggestion that the nature of rare earth ions does not influence the thermal expansion in R FeO 3 [15]. Fig.…”
Mixed ferrites Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 with orthorhombic perovskite structure isotypic with GdFeO3 were synthesized by solid-state reaction technique in air at 1473 K. Structural parameters obtained at room temperature prove a formation of continuous solid solutions in the SmFeO3–PrFeO3 and SmFeO3–NdFeO3 pseudo-binary systems. Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 show strongly anisotropic nonlinear thermal expansion: thermal expansion in the b direction is twice lower than in the a and c directions. The average linear thermal expansion coefficients of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10−6 K−1, which is close to the values reported for the parent RFeO3 compounds. Subtle anomalies in the lattice expansion of Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 detected at 650–750 K reflect magnetoelastic coupling at the magnetic ordering temperature TN.
“…4shows the phase evolution during the thermal decomposition of the colourless (Bi 25 Fe)gel. The gel was heated in static air with a rate of 5 K min −1 and a soaking time of 2 h. As shown elsewhere[37] the decomposition of the (Bi 25 Fe)-gel is a combustion-like reaction in which the starch acts as fuel and the nitrate ions as oxidizer. Heating at 300 °C(Fig.…”
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.
“…A following strong exothermic process with an onset temperature of 225 °C causes a total weight loss to 400 °C of 39.0 %. According to earlier investigations [26] the exothermic reaction suggests a selfcombustion like process in which the nitrate ions act as an oxidizing agent and the (partly decomposed) starch and glycine molecules as well as the acetate ions as fuels. A following weight loss up to about 600 °C causes a total loss of 41.3 %.…”
Section: Powder Characterization Tg-dta Xrd and Uv−vismentioning
The synthesis of nano-crystalline CuFe2O4 powders by a combustion-like process isdescribed herein. Phase formation and evolution of the crystallite size during thedecomposition process of a (CuFe2)-precursor gel were monitored up to 1000 °C. Phase-purenano-sized CuFe2O4 powders were obtained after reaction at 750 °C for 2 h resulting in acrystallite size of 36 nm, which increases to 96 nm after calcining at 1000 °C. The activationenergy of the crystallite growth process was calculated as 389 kJ mol−1. The tetragonal -cubic phase transition occurs between 402 and 419 °C and the enthalpy change (dH) wasfound to range between 1020 and 1229 J mol−1 depending on the calcination temperature. The optical band gap depends on the calcination temperature and was found between 2.03 and1.89 eV. The shrinkage and sintering behaviour of compacted powders were examined. Denseceramic bodies can be obtained either after conventional sintering at 950 °C or after a twostepsintering process at 800 °C. Magnetic measurements of both powders and correspondingceramic bodies show that the saturation magnetization rises with increasing calcination-/sintering temperature up to 49.1 emu g−1 (2.1 μB f.u.−1), whereas the coercivity and remanencevalues decrease.
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