Superconductivity in iron silicide Lu2Fe3Si5 probed by radiation-induced disordering

Resistivity r(T), Hall coefficient RH(T), superconducting temperature Tc, and the slope of the upper critical field -dHc2/dT were studied in poly- and single-crystalline samples of the Fe-based superconductor Lu2Fe3Si5 irradiated by fast neutrons. Atomic disordering induced by the neutron irradiation leads to a fast suppression of Tc similarly to the case of doping of Lu2Fe3Si5 with magnetic (Dy) and non-magnetic (Sc, Y) impurities. The same effect was observed in a novel FeAs-based superconductor La(O-F)FeAs after irradiation. Such behavior is accounted for by strong pair breaking that is traceable to scattering at non-magnetic impurities or radiation defects in unconventional superconductors. In such superconductors the sign of the order parameter changes between the different Fermi sheets (s+- model). Some relations that are specified for the properties of the normal and superconducting states in high-temperature superconductors are also observed in Lu2Fe3Si5. The first is the relationship -dHc2/dT ~ Tc, instead of the one expected for dirty superconductors -dHc2/dT ~ r0. The second is a correlation between the low-temperature linear coefficient a in the resistivity r = r0 + a1T, which appears presumably due to the scattering at magnetic fluctuations, and Tc; this correlation being an evidence of a tight relation between the superconductivity and magnetism. The data point to an unconventional (non-fononic) mechanism of superconductivity in Lu2Fe3Si5, and, probably, in some other Fe-based compounds, which can be fruitfully studied via the radiation-induced disordering.Comment: 7 pages, 8 figure

Structural Features of Cast and Quenched Cobalt–Niobium Alloys

Методами металлографии и EBSD-анализа исследованы особенности формирования структуры при b>a (ГЦК>ГПУ)-полиморфном превращении в бинарном сплаве Co–3,5Nb. Показано, что при постепенном охлаждении закристаллизовавшегося слитка в каждом b-зерне сплава происходит зарождение кристаллов a-фазы нескольких ориентаций из 4 возможных в соответствии с ориентационными соотношениями Вассермана. Разориентация субструктуры по длине кристаллов в литом сплаве не превышает 1°. После закалки структура сплава Co–3,5Nb заметно измельчается. При этом в несколько раз возрастает разориентация элементов субструктуры по длине мартенситных кристаллов, что является следствием высокого уровня закалочных микронапряжений.Specific features of structure formation at the b>a (fcc>hcp) polymorphic transformation in Co–3.5Nb binary alloy have been investigated by metallography, scanning and transmission electron microscopies, and electron backscattering diffraction analysis. It is shown that gradual cooling of a crystallized ingot induces nucleation of .-phase crystals of several orientations (of the four ones that are possible in correspondence with the Wassermann orientation relationships) in each b-grain of the alloy. Misorientation of the substructure along the martensite-crystal length in the cast alloys does not exceed 1°. After subsequent quenching, the structure of Co–Nb alloy becomes significantly refined. In addition, misorientation of substructure elements along the martensite-crystal length increases several times, which is a consequence of the high level of quenching microstress in martensite.Исследование выполнено в рамках государственного задания по теме «Структура» (№ г. р. АААА-А18-118020190116-6).The study was carried out within the framework of the state task on the topic “Structure” (no. G. R. AAAA18-118020190116-6)

THE STRUCTURE OF ALPHA-PHASE OF HAFNIUM AND HAFNIUM–TITANIUM ALLOYS

The structure of hafnium and Hf55Ti45 and Hf30Ti70 alloys formed under different kinetic conditions of polymorphic transformation was studied by metallography and EBSD analysis. The structure of the a-phase of cast hafnium and of the Hf–Ti alloys consists of packet martensite. Irrespective of the cooling rate upon transformation, within the initial grain, the same set of orientations of the a-phase occurs.Методами металлографии и EBSD.анализа изучена структура выращенного методом «плавающей зоны» гафния и сплавов Hf55Ti45 и Hf30Ti70, сформировавшаяся в разных кинетических условиях реализации полиморфного превращения. Структура a‑фазы литого гафния состоит из реек, сгруппированных в пакеты. Независимо от скорости охлаждения сплавов Hf–Ti в пределах зерна реализуется одинаковый набор ориентировок a‑фазы.Работа выполнена в рамках государственного задания по темам «Структура» (№ АААА-А18-118020190116-6) и «Давление» (№ АААА-А18-118020190104-3)