High-pressure growth of fluorine-free SmFeAsO_1−xsuperconducting single crystals

Abstract

Superconducting single crystals of SmFeAsO 1-x without fluorine doping were grown at a pressure of 3.3 GPa and a temperature of 1350-1450 °C by using the selfflux method. Plate-like single crystals of a few-150 μm in their lateral size were obtained. Single crystals showed the superconducting transition at about 53.5 K with a narrow transition width of 0.5 K. The synchrotron-irradiated x-ray diffractometry patterns and high-angle-annular-dark-field scanning transmission electron microscopy images point to the high quality of the crystals with a well-defined layered tetragonal structure. The chemical compositions of the crystals were estimated by using the electron-probe x-ray microanalysis.

Growth and annealing effect of Co-doped BaFe2As2 single crystals

“…The parent phases 122 show no superconductivity but it appears under high pressure conditions [9]. However, all these crystals with dimension less than 1 mm can be obtained using NaCl, NaAs or Sn as flux [10][11][12][13][14], but comparatively, it is feasible to grow Co and Ni doped 122 phase single crystals with large dimension and high quality [15]. Very recently, many efforts for exploring the fundamental physical properties by such approaches of neutron scattering [16], scanning tunneling microscopy [17], and angel resolved photoemission [18], have been focused on the 122 phase single crystals.…”

Flux growth at ambient pressure of millimeter-sized single crystals of LaFeAsO, LaFeAsO1−xFx, and LaFe1−xCoxAsO

“…Although the 1111 system was discovered earlier and manifests a higher T c , the focus of the scientific community has shifted toward the 122 systems because (1) sizeable high quality single crystals of the 122 system have been successfully produced by many groups and both electron and hole doping can be systematically manipulated, 5,6,7,8,9,10,11,12,13,14 and (2) the growth of large single crystals of the 1111 system has been proven to be difficult so that the largest crystals are still in submillimeter size despite tremendous efforts. 15,16,17 Under ambient pressure, plate-like NdFeAsO 1-x F x crystals with the lateral size ranging from 5 to 30 µm and thickness of 1 -5 µm can be grown by the flux method using NaCl as the flux. 17 The growth takes 10 days to homogenize at 1050 ⁰C which suggests the solubility of NdFeAsO in NaCl flux is quite limited at this temperature.…”

Absence of a Tunneling Character in c-axis Transport of SmFeAsO0.85 Single Crystals

“…The discrepancy of T c between the devices D1 and D3, fabricated out of crystals of the same batch, is presumably due to local variations of the oxygen vacancies in in the junction for D1 in a three-terminal configuration leads to more accurate normalstate transport properties. The value of  c , measured from the device D1, is three orders of magnitude larger than the ab-plane resistivity  ab ~ 0.08 m·cm for our SmFeAsO 0.85 single crystals [14]. Monotonous decrease of  c with decreasing temperature above T c suggests the metallic characteristics of the c-axis transport of our crystals rather than the semiconducting behavior, which is generally observed in the caxis transport of Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) single crystals, except for overdoped regime [16].…”

“…GPa) conditions with stoichiometric starting materials of SmAs, Fe 2 O 3 , and Fe. Details of the single-crystal growth are described in our previous report [14]. Plate-like single crystals with lateral size of 7 -10 m and thickness of 0.5 -2 m were attached onto sapphire substrates using negative photoresist.…”