Исследовалось влияние термомеханических циклов (сжатие вдоль направления [011]--возврат деформации памяти формы при нагреве кристалла) на вид и характеристики диаграмм сжатия кристаллов сплава Ni49Fe18Ga27Co6, не подвергнутых после роста высокотемпературному отжигу и закалке в воду. Найдено, что в течение первых девяти циклов эти характеристики непостоянны. Начиная с десятого термомеханического цикла они становятся стабильными, а кристаллы по деформационным свойствам становятся аналогичными закаленным кристаллам этого сплава. Это означает, что в процессе термомеханического циклирования происходит диспергирование антифазных нанодоменов дислокациями, в результате чего неупорядоченная B2-структура кристалла превращается в упорядоченную L21-структуру, характерную для закаленных кристаллов. Ключевые слова: диаграмма сжатия кристалла, деформация памяти формы, упорядоченная и неупорядоченная структура сплава.
Record thick (up to 100 μm) epitaxial layers of a prospective metastable semiconductor Ga2O3 were grown by HVPE (Halide Vapor Phase Epitaxy) on GaN buffer layers on c-sapphire substrates. The X-ray diffraction pattern of the layers show that the structure of the layer is a pure kappa(ε)-Ga2O3 without any other phases. At the same time, the organization of a domain structure was observed, which manifests itself in the form of pseudohexagonal prisms that retain the orientation of the gallium nitride sublayer. Schottky diodes with nickel contacts were fabricated and the electrical and photoelectric properties of the layers were studied. Capacitance-voltage (C-V) and frequency-capacitance (C-f) dependencies were studied, photocurrent and photocapacitance spectra were measured. Keywords: Gallium oxide, HVPE, epitaxial layers, sapphire substrates.
Shape memory effects in Ni55Fe18Ga27 single crystal grown along the [001] direction by the Czochralski method was studied. It was found that deformation of [001] single crystal in the martensite state was realised via reorientation of 10 M martensite and stress-induced transformations: 10 M → 14 M → L10. On unloading, the reverse L10 → 14 M → 10 M transformations occurred and a large unelastic strain recovered. On heating, the oriented 10 M martensite transformed to the L21 austenite phase and the shape memory effect was observed. An increase in preliminary strain resulted in an increase in the shape memory effect value to 4.6%. The [001] Ni55Fe18Ga27 alloy single crystal demonstrated transformation plasticity and shape memory effects on cooling and heating under stress however, an increase in stress decreased the values of these effects. This was caused by stress-induced martensite appearing in the sample during loading in the austenite state, which decreased the volume of the austenite phase that could undergo the martensitic transformation on cooling. The [001] Ni55Fe18Ga27 alloy single crystal demonstrated a two-way shape memory effect and its value depended on the residual strain in a non-monotonic way and the maximum recoverable strain was 0.7%.
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