Electric Conductivity and Gas-Sensing Properties of Nickel Ferrite Thin Films Formed by Ion-Beam Sputtering Deposition

Ferrites with composition of NiMnxFe1-xO4, (with x = 0 ÷ 1.0) have been synthesized by self-propagating high-temperature synthesis (SHS). The particle size of the synthesized ferrite powder was about 10 nm. Additional heat treatment at 1270 K during 50 min allowed us to obtained product with the single phase composition NiFe2O4.  We found out that the increasing of the manganese content (x) increased the lattice constant of the ferrites from 0.833896 nm (x = 0) up to 0.836369 nm (x = 1). The synthesized powder contains two types of ferrite particles that are varied in size and shape. The magnetic properties significantly depend on the microstructure and chemical composition of synthesized ferrites. It has been found that the coercive force Hc increased from 1.75 (x = 0.2) to 2.85 (x = 1). By using of IBSD technology thin film of NiFe2O4 was sputtered on the Si (100) substrate. All sputtered films were X-ray transparent. The structure of ferrite films consisted of agglomerate less than 35 nm. The thickness of the sputtered film was about 600 nm. Additional heat treatment at 770 K during 90 min resulted to homogeneity of the film microstructure. The temperature range 400-750 K corresponds to working temperature range of gas-sensing devices. The ferrite compounds were studied by TOF-SIMS (Time-of-Flight Secondary-Ion-Mass-Spectrometry) for all depth of film. The resistivity R of synthesized film was 39 kΩ. Measurement of gas-sensing sensitivity RCH4/Rair for gas (2%v. CH4) – air mixture showed increase of R up to 12% at the present of methane at 403 K. For further research we plan to replace iron to manganese ions in chemical compounds of ferrite

Синтез интерметаллидного сплава на основе системы Cu–Ti–Al. Структурно-фазовый анализ и электрофизические свойства

For the first time, an intermetallic alloy based on the Heusler phase – Cu2TiAl – was obtained by self-propagating high-temperature synthesis (SHS) in the Cu–Ti–Al reaction mixture. The frontal combustion modes of green mixture compositions and phase formation processes during synthesis were studied. The products obtained were studied by X-ray diffraction analysis including high-temperature diffractometry with stage heating up to 900 K, scanning electron microscopy, differential thermal analysis (DTA), and some physical properties were studied. Also, electrophysical and magnetic measurements were carried out for the obtained alloy. The results of X-ray analysis and SEM using energy-dispersive analysis (EDA) showed that the Heusler phase content in the synthesized product is at least 82 %. The product also contains copper (Cu9Al4) and titanium (Ti3Al2) aluminides. The temperature dependence of the synthesized product electrical resistivity was measured for a wide temperature range of 90–1000 K, which was 0.3 μmm at T = 300 K. The metallic type of the conductivity for the samples obtained and the abnormal behavior of the electrical resistance temperature curve in the region of Т = 770÷790 K were revealed. Thermal analysis was used to measure the melting point of the synthesized product and to reveal additional heat effects at Т = 788, 848 and 1248 К associated with possible phase transitions in the Cu2TiAl intermetallic compound. A possible mechanism of phase transitions is considered in accordance with the Cu–Ti–Al system phase diagram. Magnetic measurements results showed that intermetallic samples obtained by the SHS method feature by weak ferromagnetic properties with residual magnetization of 0.069 A·m2/kg.Методом самораспространяющегося высокотемпературного синтеза (СВС) реакционной смеси системы Cu–Ti–Al впервые получен интерметаллидный сплав на основе фазы Гейслера – Cu2TiAl. Изучены режимы фронтального горения шихтовых составов системы и процессы формирования фаз при синтезе. Полученные продукты исследовались методами рентгено- фазового анализа (РФА), включая высокотемпературную дифрактометрию со ступенчатым нагревом до 900 К, сканирующей электронной микроскопии (СЭМ) и дифференциально-термического анализа, изучались физические свойства. Кроме того, для полученного сплава были проведены электрофизические и магнитные измерения. Результаты РФА и СЭМ с использованием энергодисперсионного анализа показали, что содержание фазы Гейслера в синтезированном продукте составляет не менее 82 %. В составе продукта также присутствуют алюминиды меди (Cu9Al4) и титана (Ti3Al2). Проведено измерение температур- ной зависимости удельного электросопротивления синтезированного продукта для широкого диапазона температур 90– 1000 К, которое при Т = 300 К составило 0,3 мкмОм·м. Выявлены металлический характер проводимости для полученных образцов и аномальное поведение температурной кривой электросопротивления в диапазоне Т = 770÷790 К. Методом термического анализа измерена температура плавления синтезированного продукта и обнаружены дополнительные тепловые эффекты при Т = 788, 848 и 1248 К, связанные с возможными фазовыми переходами в интерметаллиде Cu2TiAl. Рассмотрен возможный механизм фазовых переходов в соответствии с диаграммой фазового равновесия системы Cu–Ti–Al. Результаты магнитных измерений показали, что образцы интерметаллида, полученного методом СВС, проявляют слабые ферромагнитные свойства с остаточной намагниченностью 0,0069 А·м2/кг