High-Pressure Synthesis of Superconducting Sn3S4 Using a Diamond Anvil Cell with a Boron-Doped Diamond Heater.

High-pressure techniques open exploration of functional materials in broad research fields. An established diamond anvil cell with a boron-doped diamond heater and transport measurement terminals has performed the high-pressure synthesis of a cubic Sn3S4 superconductor. X-ray diffraction and Raman spectroscopy reveal that the Sn3S4 phase is stable in the pressure range of P > 5 GPa in a decompression process. Transport measurement terminals in the diamond anvil cell detect a metallic nature and superconductivity in the synthesized Sn3S4 with a maximum onset transition temperature (Tconset) of 13.3 K at 5.6 GPa. The observed pressure-Tc relationship is consistent with that from the first-principles calculation. The observation of superconductivity in Sn3S4 opens further materials exploration under high-temperature and -pressure conditions.

Phase Relationship of Mg2Si at High Pressures and High Temperatures and Thermoelectric Properties of Mg9Si5.

Magnesium silicide (Mg2Si) is a promising eco-friendly thermoelectric material, which has been extensively studied in recent times. However, its phase behavior at high pressures and temperatures remains unclear. To this end, in this study, in situ X-ray diffraction analysis was conducted at high pressures ranging from 0 to 11.3 GPa and high temperatures ranging from 296 to 1524 K, followed by quenching. The antifluorite-phase Mg2Si decomposed to Mg9Si5 and Mg at pressures above 3 GPa and temperatures above 970 K. The antifluorite-phase Mg2Si underwent a structural phase transition to yield a high-pressure room-temperature (HPRT) phase at pressures above 10.5 GPa and at room temperature. This HPRT phase also decomposed to Mg9Si5 and Mg when heated at ∼11 GPa. When 5Mg2Si decomposed to Mg9Si5 and Mg, the volume reduced by ∼6%. Mg9Si5 synthesized at high pressures and high temperatures was quenchable under ambient conditions. Thermoelectric property measurements of Mg9Si5 at temperatures ranging from 10 to 390 K revealed that it was a p-type semiconductor having a dimensionless thermoelectric figure of merit (ZT) of 3.4 × 10-4 at 283 K.

Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl.

We report the magnetism and transport properties of the Heusler compound Fe2+x V1-x Al at -0.10 ⩽ x ⩽ 0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x ≈ -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P - P c ) (γ) . At x ⩽ -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x ≈ 0.05, itinerant ferromagnetism was established. At the quantum critical points at x = -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

Possibility of charge density wave transition in a SrPt2Sb2 superconductor.

The first-order transition at T(0) = 270 K for the platinum-based SrPt2Sb2 superconductor was investigated using x-ray diffraction and magnetic susceptibility measurements. When polycrystalline SrPt2Sb2 was cooled down through T(0), the structure was transformed from monoclinic to a modulated orthorhombic structure, and no magnetic order was formed, which illustrates the possibility of a charge density wave (CDW) transition at T(0). SrPt2Sb2 can thus be a new example to examine the interplay of CDW and superconductivity in addition to SrPt2As2, BaPt2As2, and LaPt2Si2. It is unique that the average structure of the low-temperature phase has higher symmetry than that of the high-temperature phase.

Structural characterization of magnesium-based compounds Mg9Si5 and Mg4Si3Al (superconductor) synthesized under high pressure and high temperature conditions.

Two kinds of magnesium-based compounds Mg9Si5 and Mg4Si3Al have been prepared under high pressure and high temperature (HPHT) conditions of 5 GPa at 900-1100 °C. Single crystal study revealed that Mg9Si5 crystallizes in space group P6(3) (No. 173) with the lattice parameters a = 12.411(1) Å, c = 12.345(1) Å, and Z = 6. The structure can be derived from the high pressure form Mg2Si with the anticotunnite structure; excess Si atoms of Mg9Si5 form Si-Si pairs in the prismatic cotunnite columns running along the c axis. Mg4Si3Al is obtained by a rapid cooling of a ternary mixture Mg:Al:Si = 1:1:1 from ~800 °C to room temperature under a pressure of 5 GPa. The compound crystallizes in space group P4/ncc (No. 130) with the lattice parameters a = 6.7225(5) Å, c = 13.5150(9) Å, and Z = 4. The structure consists of an alternate stacking of [AlSi2] layers having a Cairo pattern and [Mg4Si] antitetragonal prismatic layers. It can be viewed as composed of hexa-Si-capped tetragonal prismatic cages Mg8Si6 with an Al atom at the center of each cage, Al@Mg8Si6. The compound shows superconductivity with a transition temperature Tc = 5.2 K. The formation regions of the two kinds of new magnesium-based compounds have been proposed.

Semiconducting behavior of type-I Si clathrate K8Ga8Si38.

A ternary type-I Si clathrate K(8)Ga(8)Si(38) has been revealed to be an indirect band gap semiconducting material with an energy gap (E(g)) of approximately 0.10 eV, which is much smaller than the calculated E(g) value that is 0.15 eV wider than E(g) of elemental Si with the diamond-type structure.

In situ observation of the formation of Si clathrate Ba8Si46 at high pressures and high temperatures.

X-ray diffraction measurements at high pressures and high temperatures revealed that Si clathrate Ba 8Si 46 is formed by a solid-phase reaction of an 8:30 molar mixture of SrSi 2-phase BaSi 2 and Si after BaSi 2 undergoes the BaSi 2-to-EuGe 2 and the EuGe 2-to-SrSi 2 transitions. The volume reduction during the formation of Ba 8Si 46 is the largest, 7.6%, among the observed transitions. On the other hand, an 8:30 molar mixture of SrSi 2-phase SrSi 2 and Si does not result in the formation of Sr 8Si 46 at high pressures and high temperatures; only SrSi 2 transforms from the SrSi 2 phase into the alpha-ThSi 2 phase, and Si remains in the diamond phase.

Electrical properties of single-crystalline CaAl2Si2.

Electrical resistivity and Hall coefficient measurements of single-crystalline CaAl(2)Si(2) revealed that CaAl(2)Si(2) is a metal in which both electrons and holes contribute to the transport properties; its dominant carriers are holes at temperature below 150 K but electrons above that temperature.