Growth and structure of superconducting FeSe crystals
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Growth and Structure of Superconducting FeSe Crystals J. I. Gorinaa, G. A. Kaluzhnayaa, M. V. Golubkova, V. V. Rodina, N. N. Sentjurinaa, and S. G. Chernooka, b a b
Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia Fiber Optics Research Center, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119333 Russia email: [email protected] Received June 27, 2011
Abstract—Superconducting crystals of iron selenide FeSe are grown and their phase and elemental compo sitions are studied. The structural analysis of individual FeSe1 – x crystals showed the coexistence of two phases in this compound. The resistivities and magnetic susceptibilities of the crystals are investigated. DOI: 10.1134/S1063774512040050
The recent discovery of superconductivity in Fe pnictides RFeAsO1 – xFx (R = La, Nd, or Sm) [1–3] and chalcogenides FeSe and FeSe1 – xTex [4–6] has initiated intensive studies of these materials, whose superconducting properties are determined by Fe–As and Fe–Se layers, respectively. The interest in the FeSe and FeSeTe compounds is caused by the relative simplicity of their crystal structures and the fact that they have much lower toxicity than Fe pnictides. Many researchers use FeSe as a model system to study the mechanisms of superconductivity in Fe pnictides and chalcogenides [4–7]. FeSe, a compound of variable composition, is known to exist in two modifications, one of which is the superconducting tetragonal phase of the PbO (βFeSe) structural type with Tc = 8–10 K and the other is a nonsuperconducting hexagonal FeSe phase with a NiAs (δFeSe) structure [6]. Figure 1 shows a fragment of the combined phase diagram of the Fe–Se system: the lines are taken from the diagram presented in [8], and the composition range near 49.5 at % shows that βFeSe is implemented in a narrow homogeneity region near the stoichiometric composition Fe : Se = 1 : 1 from the Fe side [8]. Since the nonsuperconduct ing δFeSe phase crystallizes at a temperature of 1075°C and the superconducting βFeSe phase is formed below 450°C, in several studies the crystals were grown from a flux [9, 10] and from the gas phase [11]. The data on the composition, homogeneity region, and superconducting properties of FeSe1 – x obtained in different works differ significantly (appar ently due to the different growth conditions for iron selenide).
analyze their structure by Xray diffraction, composi tion including the distribution of elements over the sample surface and investigate their physical proper ties, specifically, the components of resistivity in the directions along and perpendicularly to the crystal planes, as well as their magnetic susceptibility. The crystal structure was studied on a DRON2.0 diffractometer (CuKα radiation) with a graphite monochromator. Individual platelike crystals were investigated. The morphology and composition of the crystals were studied on a JSM5910LV scanning electron microscope equipped with an Xray energydispersive analyzer (Oxford Instruments)
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