TY - JOUR
T1 - Metastable magnesium titanate phases synthesized in nanometric systems
AU - Zabicky, Jacob
AU - Frage, Naum
AU - Kimmel, Giora
AU - Hazan, Niva
AU - El-Fahel, Hanie
AU - Goncharov, Elena
AU - Manor, Eitan
AU - Shneck, Roni
N1 - Funding Information:
ACKNOWLEDGEMENTS The authors acknowledge partial support of this research by the Ministry of Science and the Arts of the State of Israel and the Helen Tzoref Applied Research Grant Programme. The authors thank Mr M. Albert of Microelectronics Ltd for dielectric measurements, and Mrs E. Shuabi and Mrs T. Reich for assistance in the synthesis of sol-gel precursors.
PY - 1997/1/1
Y1 - 1997/1/1
N2 - When heating mixtures of conventional magnesia and titania powders, geikielite (MgO. TiO2) appears first at about 600°C; only above 1200–1300°C is either qandilite (2MgO. TiO2) or karrooite (MgO. 2TiO2) formed, depending on whether MgO or TiO2is in excess. A different behaviour pattern is observed when starting from nanometre precursors, consisting of hydroxides of magnesium and itanium, which lose water on heating to about 400°C, yielding nanocrystalline oxides. Coprecipitated nanometre precursors yield at 600°C qandilite, geikielite or karrooite, depending on the relative stoichiometries of magnesia and titania in the precursor powder. At higher temperatures, up to 1200°C geikielite is the only titanate formed, and only above 1300°C does qandilite or karrooite reappear, depending on the stoichiometry of the original mixture. Only karrooite is formed when independently prepared nanometre precursors of magnesia and titania are mixed together and heated to temperatures as low as 400°C and up to 600°C, the stoichiometric ratio of the mixture notwithstanding. Estimation of surface area changes taking place when nanometre particles coalesce with each other to form magnesium titanates show that substantial reductions in surface energy take place, even if the products remain of nanometre size. Such reductions depend on the absolute and relative particle sizes of the reacting oxides and the stoichiometry of the final product. The contribution of diffusion processes, surface energy and misfit volume to the formation of the various magnesium titanates from the oxides is discussed. All three magnesium titanates synthesized from nanometre precursors show a stable dielectric constant e over a wide range of frequencies, in contrast with an equivalent commerical powder used in the manufacture of microcondensers. Furthermore, the quality factorQof magnesium orthotitanate (geikielite) synthesised from nanometre precursors is higher by about one order of magnitude than that of the commercial product.
AB - When heating mixtures of conventional magnesia and titania powders, geikielite (MgO. TiO2) appears first at about 600°C; only above 1200–1300°C is either qandilite (2MgO. TiO2) or karrooite (MgO. 2TiO2) formed, depending on whether MgO or TiO2is in excess. A different behaviour pattern is observed when starting from nanometre precursors, consisting of hydroxides of magnesium and itanium, which lose water on heating to about 400°C, yielding nanocrystalline oxides. Coprecipitated nanometre precursors yield at 600°C qandilite, geikielite or karrooite, depending on the relative stoichiometries of magnesia and titania in the precursor powder. At higher temperatures, up to 1200°C geikielite is the only titanate formed, and only above 1300°C does qandilite or karrooite reappear, depending on the stoichiometry of the original mixture. Only karrooite is formed when independently prepared nanometre precursors of magnesia and titania are mixed together and heated to temperatures as low as 400°C and up to 600°C, the stoichiometric ratio of the mixture notwithstanding. Estimation of surface area changes taking place when nanometre particles coalesce with each other to form magnesium titanates show that substantial reductions in surface energy take place, even if the products remain of nanometre size. Such reductions depend on the absolute and relative particle sizes of the reacting oxides and the stoichiometry of the final product. The contribution of diffusion processes, surface energy and misfit volume to the formation of the various magnesium titanates from the oxides is discussed. All three magnesium titanates synthesized from nanometre precursors show a stable dielectric constant e over a wide range of frequencies, in contrast with an equivalent commerical powder used in the manufacture of microcondensers. Furthermore, the quality factorQof magnesium orthotitanate (geikielite) synthesised from nanometre precursors is higher by about one order of magnitude than that of the commercial product.
UR - http://www.scopus.com/inward/record.url?scp=0006726531&partnerID=8YFLogxK
U2 - 10.1080/01418639708241126
DO - 10.1080/01418639708241126
M3 - Article
AN - SCOPUS:0006726531
SN - 1364-2812
VL - 76
SP - 605
EP - 614
JO - Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties
JF - Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties
IS - 4
ER -