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The optical and magnetic properties of nano-LaFeO 3 powders prepared by a starch assisted soft-chemistry synthesis and corresponding ceramics have been investigated. Magnetic measurements on LaFeO 3 powders with crystallite sizes of 37−166 nm show pronounced magnetization hysteresis loops. Measurements at 300 K reveal that the coercivity (H c) of 19−32 kOe depends on the crystallite size, whereas the low remanence values (M r) of roughly 0.2 emu/g and the maximal magnetization (M max) at 90 kOe of 1.05−0.85 emu/g are only slightly changing. Investigations at 10 K reveal a loop shift (exchange bias) up to 12 kOe in the negative direction depending on the crystallite size. Ceramic bodies, sintered at ≥ 1300 °C possess a considerably reduced hysteresis loop. H c is decreased up to 3.0 kOe, whereas M r 2 and M max are slightly increasing. None of the samples reaches saturation at 90 kOe indicating an anti-ferromagnetic ordering of the spins. The optical band gaps of the LaFeO 3 samples were determined by means of diffuse reflectance spectra. For all LaFeO 3 powders similar band gaps of 2.65 eV were observed. However, ceramics with grain-size significantly larger than 250 nm show smaller band gap values up to 2.12 eV.

The thermal decomposition of Ba,Ti-precursor complexes, containing organic ligands and suitable for the single-source preparation of nanocrystalline BaTiO 3 , leads firstly to the segregation of specific Ba-rich and Ti-rich phases. Quantitative electron energy loss spectroscopy and powder X-ray diffraction data indicated that the (i) Ba-rich phase is a BaOstabilised variant of the calcite-type high-temperature modification of BaCO 3 and (ii) Ti-rich phases are represented by low crystalline barium titanates with the general Ba:Ti ratio close to 1:4. The subsequent solid state reaction between these phases results then in the formation of BaTiO 3 .

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.

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Crystallite-growth, phase transition, magnetic properties, and sintering behaviour of nano-CuFe2O4 powders prepared by a combustion-like process. Journal of Solid State Chemistry, Elsevier, 2014, 213, pp.Abstract. The synthesis of nano-crystalline CuFe 2 O 4 powders by a combustion-like process is described herein. Phase formation and evolution of the crystallite size during the decomposition process of a (CuFe 2 )-precursor gel were monitored up to 1000 °C. Phase-pure nano-sized CuFe 2 O 4 powders were obtained after reaction at 750 °C for 2 h resulting in a crystallite size of 36 nm, which increases to 96 nm after calcining at 1000 °C. The activation energy 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 (∆H) was found to range between 1020 and 1229 J mol −1 depending on the calcination temperature. The 2 optical band gap depends on the calcination temperature and was found between 2.03 and 1.89 eV. The shrinkage and sintering behaviour of compacted powders were examined. Dense ceramic bodies can be obtained either after conventional sintering at 950 °C or after a twostep sintering process at 800 °C. Magnetic measurements of both powders and corresponding ceramic bodies show that the saturation magnetization rises with increasing calcination-/ sintering temperature up to 49.1 emu g −1 (2.1 µ B f.u. −1 ), whereas the coercivity and remanence values decrease.

The formation of solid solutions of the type [Ba(HOC 2 H 4 OH) 4 ][Ti 1x Ge x (OC 2 H 4 O) 3 ] as Ba(Ti 1-x /Ge x)O 3 precursors and the phase evolution during thermal decomposition of [Ba(HOC 2 H 4 OH) 4 ][Ti 0.9 Ge 0.1 (OC 2 H 4 O) 3 ] (1) are described herein. The 1,2ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO 3 and BaGeO 3. A heating rate controlled calcination procedure up to 730 °C leads to a nm-sized Ba(Ti 0.9 /Ge 0.1)O 3 powder (1a) with a specific surface area of S = 16.9 m 2 /g, whereas a constant heating rate calcination at 1000 °C for 2 h yields a powder (1b) of S = 3.0 m 2 /g. The shrinkage and sintering behaviour of the resulting Ba(Ti 0.9 /Ge 0.1)O 3 powder compacts in comparison with nm-sized BaTiO 3 powder compacts (2a) has been investigated. A 2-step sintering procedure of nm-sized Ba(Ti 0.9 /Ge 0.1)O 3 compacts (1a) leads below 900 °C to ceramic bodies with a relative density of ≥ 90 %. Furthermore, the cubic tetragonal phase transition temperature has been detected by dilatometry and the temperature dependence of the dielectric constant (relative permittivity) has also been measured.

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. Calcinations to 1000 °C result in crystallite sizes up to 166 nm. Dilatometric measurements of the sintering behaviour show that the beginning of shrinkage of pellets from the nano-sized powder is downshifted by more than 300 °C compared to coarse-grained mixed-oxide powder. The orthorhombic rhombohedral phase transition was observed at 980 °C in DTA measurements for coarse-grained ceramic bodies. The enthalpy change (∆H) during the phase transition and the thermal expansion coefficient (α dil) for ceramics was determined as 410 J/mol and 11.8⋅10-6 K-1 , respectively. Whereas the enthalpy changes during the phase transition of the nano-sized LaFeO 3 powders are ≤ 200 J/mol.