Pressure-induced superconductivity and structural transitions in Ba(Fe

Electrical transport and structural characterizations of isoelectronically substituted Ba(Fe0.9Ru0.1)2As2 have been performed as a function of pressure up to ~30 GPa and temperature down to ~10 K using designer diamond anvil cell. Similar to undoped members of the AFe2As2 (A = Ca, Sr, Ba) family, Ba(Fe0.9Ru0.1)2As2 shows anomalous a-lattice parameter expansion with increasing pressure and a concurrent ThCr2Si2 type isostructural (I4/mmm) phase transition from tetragonal (T) phase to a collapsed tetragonal (cT) phase occurring between 12 and 17 GPa where the a is maximum. Above 17 GPa, the material remains in the cT phase up to 30 GPa at 200 K. The resistance measurements show evidence of pressure-induced zero resistance that may be indicative of high-temperature superconductivity for pressures above 3.9 GPa. The onset of the resistive transition temperature decreases gradually with increasing pressure before completely disappearing for pressures above ~10.6 GPa near the T-cT transition. We have determined the crystal structure of the high-Tc phase of Ru-doped BaFe2As2 to remain as tetragonal (I4/mmm) by analyzing the X-ray diffraction pattern obtained at 10 K and 9.7 ± 0.7 GPa, as opposed to inferring the structural transition from electrical resistance measurement, as in a previous report [S.K. Kim, M.S. Torikachvili, E. Colombier, A. Thaler, S.L. Bud’ko, P.C. Canfield, Phys. Rev. B 84, 134525 (2011)]

Nanocrystalline diamond micro-anvil grown on single crystal diamond as a generator of ultra-high pressures

By combining mask-less lithography and chemical vapor deposition (CVD) techniques, a novel two-stage diamond anvil has been fabricated. A nanocrystalline diamond (NCD) micro-anvil 30 μm in diameter was grown at the center of a [100]-oriented, diamond anvil by utilizing microwave plasma CVD method. The NCD micro-anvil has a diamond grain size of 115 nm and micro-focused Raman and X-ray Photoelectron spectroscopy analysis indicate sp3-bonded diamond content of 72%. These CVD grown NCD micro-anvils were tested in an opposed anvil configuration and the transition metals osmium and tungsten were compressed to high pressures of 264 GPa in a diamond anvil cell