Abstract. J. Solid State Chem. 217 (2014) 50–56. (DOI: 10.1016/j.jssc.2014.05.006). The syntheses of phase−pure and stoichiometric iron sillenite (Bi25FeO40) 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 thecombustion−like process leads to pure Bi25FeO40 after calcination at 750 °C for 2 h (2a). The activation energy of the crystallite growth process ...
Abstract. J. Mater. Sci. 53 (2018) 1024–1034. (DOI: 10.1007/s10853-017-1609-1). A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of com...
Abstract. J. Eur. Ceram. Soc. 37 (2017) 1509–1516. (DOI: 10.1016/j.jeurceramsoc.2016.12.014). A facile method to prepare nanoscaled BaFe0.5Nb0.5O3 via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55 m2 g−1 and a crystallite size of 15 nm. The as-prepared powder does not show anysignificant crystallite growth up to 700 °C. The activation energy of the crystallite growth process was calculated as 590 kJ mol−1. Den...
Abstract. J. Alloys Compd. 368 (2015) 141–147. (DOI: 10.1016/j.jallcom.2015.03.082). The synthesis of BaTiO3-MgFe2O4 composite powders by a Pechini-like one-pot process and resulting ceramic bodies is described herein. Phase formation during the decomposition of homogenous (Ba,Ti,Fe,Mg)-gels was monitored up to 1200 °C. Composite powders consisting of BaTiO3 and MgFe2O4 were obtained after decomposition at 700 °C for 1 h resulting in crystallite sizes of about 10 nm. The shrinkage and sin...
Abstract. J. Mater. Sci. 43 (2008) 832-838. (DOI: 10.1007/s10853-007-2195-4). The formation of solid solutions of the type [Ba(HOC2H4OH)4][Ti1-xGex(OC2H4O)3] as Ba(Ti1-x/Gex)O3 precursors and the phase evolution during thermal decomposition of [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) are described herein. The 1,2- ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO3 and BaGeO3. A heating rate controlled calcination procedure up to 730 °C leads to a nm-sized Ba(Ti0.9/Ge...
Abstract. Mater. Chem. Phys. 112 (2008) 531-535. (DOI: 10.1016/j.matchemphys.2008.06.005). The shrinkage mechanism of BaTiO3 powder compacts containing 10 mol% BaGeO3, synthesized by a precursor route and a conventional mixed-oxide method, are described herein. The calcination of a barium titanium germanium 1,2-ethanediolato complex precursor - [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) - at 730 °C leads to a nm-sized Ba(Ti0.9/Ge0.1)O3 powder (1a) (SBET = 16.9 m2/g) consisting of BaTiO3 an...
Abstract. Mater. Chem. Phys. 119 (2010) 118-122. (DOI: 10.1016/j.matchemphys.2009.08.026). Dielectric properties and the cubic tetragonal phase transition temperature of dense BaTiO3 ceramics containing 10 mol% BaGeO3, sintered between 840 and 1350 °C, have been investigated. The ceramic bodies were prepared from a nano-sized BaTi0.9/Ge0.1O3 powder consisting of both BaTiO3 and BaGeO3 phases. The addition of BaGeO3 leads to a reduction and broadening of the permittivity maximum, and to a...
Abstract: The import for oil in the whole world and particularly in Tanzania is heavily increasing due to the increasing number of cars, motorcycles, industries, and other machines for their operations. However, the imported oil has been going along with the imported inflation in the country. It is well known that a strong and stable inflation influences the economic growth of a country since it inspires investments, and enhances the consumers to afford purchasing of goods and service a...
Abstract. J. Eur. Ceram. Soc. 29 (2009) 2317-2324. (DOI: 10.1016/j.jeurceramsoc.2009.01.026). Preparation of a very fine BaSnO3 powder by calcination of a barium tin 1,2-ethanediolato complex precursor and its sintering behaviour are described herein. A rate controlled calcination process to 820 °C leads to a nm-sized BaSnO3 powder with a specific surface area of S = 15.1 m2/g (dav. = 55 nm). The powder has a slightly larger cell parameter of a = 412.22(7) pm compared to the single cryst...
Abstract. Thermochim. Acta 441 (2006) 176-183. (DOI: 10.1016/j.tca.2005.12.010). The thermal behaviour of [Ba(C2H6O2)4][Sn(C2H4O2)3] used as a BaSnO3 precursor, and its phase evolution during thermal decomposition are described. The initially formed transient barium-tin-oxycarbonate phase disintegrates into BaCO3 and SnO2, reacting subsequently to BaSnO3. The existence of the intermediate oxycarbonate phase is evidenced by FT-IR, XRD, and EELS (ELNES) investigations.
Abstract. J. Eur. Ceram. Soc. 30 (2010) 1419-1425. (DOI: 10.1016/j.jeurceramsoc.2009.12.015). DTA, XRD and sintering investigations of the system BaSnO3−BaGeO3, prepared by a mixed-oxide method, are described herein. The melting temperature of this system is about 1270 ± 5 °C. We find a partial solubility of BaGeO3 into BaSnO3 of the order of 6−7 mol%. Up to 50 mol% BaGeO3, the calcined powders (1150 °C) as well as the once-sintered samples consist of BaSnO3 and orthorhombic BaGeO3 at ...
Abstract. J. Mater. Sci. 45 (2010) 3784–3790. (DOI: 10.1007/s10853-010-4432-5). The formation of solid solutions of the type [Ba(HOC2H4OH)4][Sn1−xGex(OC2H4O)3] as BaSn1-x/GexO3 precursor and the phase evolution during its thermal decomposition are described in this paper. The 1,2-ethanediolato complexes can be decomposed to nano-sized BaSn1−x/GexO3 preceramic powders. Samples with x = 0.05 consist of only a Ba(Sn,Ge)O3 phase, whereas powders with x = 0.15 and 0.25 show diffraction patte...
Abstract. Z. Anorg. Allg. Chem. 629 (2003) 371-373. (DOI: 10.1002/zaac.200390061). Colourless single crystals of BaC4O4 have been obtained from aqueous solution at 80 °C. BaC4O4 is stable in air up to 490 °C. BaCO3 is formed by further increase of temperature. BaC4O4 crystallizes in the tetragonal space group I4/mcm (nr. 140) with a=635.95(5),c=1240.77(13) pm, Z=4. Ba2+ is coordinated by eight oxygen atoms of the squarate dianions; Ba—O 276.1(1) pm. The coordination polyhedron is a distor...
Abstract. Z. Anorg. Allg. Chem. 641 (2015) 1150–1155. (DOI: 10.1002/zaac.201500050). Monoclinic single crystals of Ba2(H2O)[μ10-C6H2(COO)4] (1) and Pb2(H2O)[μ10- C6H2(COO)4] (2) were obtained using the silica gel method [space group C2/c (no. 15), Z = 4; 1: a = 780.89(4), b = 1756.19(8), c = 914.80(5) pm, β = 114.512(5)°; 2: a = 756.70(10), b =1772.8(2), c = 890.2(2) pm, β = 113.590(10)°]. There are two crystallographically independent M2+ ions (M = Ba, Pb). M(1) is surrounded by eigh...
Abstract A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative densit...