Crystal growth, structural and superconducting properties of β-pyrochlores KOs2O6
Authors: G. Schuck, S. M. Kazakov, K. Rogacki, N. D. Zhigadlo and J. KarpinskiJournal-ref: Phys. Rev. B, 73 (2006) 144506 , PDF
Single crystals of KOs2O6 have been grown in a sealed quartz ampoule. Detailed single crystal x-ray diffraction studies at room temperature show Bragg peaks that violate Fdm symmetry. With a comparative structure refinement the structure is identified as noncentrosymmetric (F
3m). Compared to the ideal
-pyrochlore lattice (Fd
m), both Os tetrahedral and O octahedral networks exhibit breathing mode like volume changes accompanied by strong anisotropic character of the K channels. The crystals show metallic conductivity and a sharp transition to the superconducting state at Tc=9.65 K. Superconducting properties have been investigated by magnetization measurements performed in a temperature range from 2 to 12 K and in magnetic fields from 0 to 60 kOe. The temperature dependence of the upper critical field Hc2(T) has been determined and the initial slope (dHc2/dT)Tc=–33.3 kOe/K has been obtained near Tc. The upper critical field at zero temperature was estimated to be Hc2(0)
230 kOe, which is a value close to the Pauli paramagnetic limiting field Hp(0)
250 kOe. Then, the Ginzburg–Landau (GL) coherence length
GL(0)
3.8 nm was calculated, and the Maki parameter
2 was obtained, suggesting the possibility that KOs2O6 might behave unconventionally at low temperatures and high magnetic fields.