Metastable Materials Accessed under Moderate Pressure Conditions (P ≤ 3.5 GPa) in a Piston-Cylinder Press

Abstract

In this review, we describe different families of metastable materials, some of them with relevant technological applications, which can be stabilized at moderate pressures 2–3.5 GPa in a piston-cylinder press. The synthesis of some of these systems had been previously reported under higher hydrostatic pressures (6–10 GPa), but can be accessed under milder conditions in combination with reactive precursors prepared by soft-chemistry techniques. These systems include perovskites with transition metals in unusual oxidation states (e.g., RNiO3 with Ni3+, R = rare earths); double perovskites such as RCu3Mn4O12 with Jahn–Teller Cu2+ ions at A sites, pyrochlores derived from Tl2Mn2O7 with colossal magnetoresistance, pnictide skutterudites MxCo4Sb12 (M = La, Yb, Ce, Sr, K) with thermoelectric properties, or metal hydrides Mg2MHx (M = Fe, Co, Ni) and AMgH3 (A: alkali metals) with applications in hydrogen storage. The availability of substantial amounts of sample (0.5–1.5 g) allows a complete characterization of the properties of interest, including magnetic, transport, thermoelectric properties and so on, and the structural characterization by neutron or synchrotron X-ray diffraction techniques.

High-pressure synthesis, spin-glass behaviour, and magnetocaloric effects in FexTi2S4 heideite sulphides

“…Different synthesis procedures can lead to different stoichiometries, affecting the structural defects, order/disorder and vacancies, which modify the final material properties. Particularly, the high-pressure methods to synthesize new compounds have some advantages over the conventional ambient pressure methods, including stabilization of metastable phases with unusual valence states and enhanced densification 26 . In this paper, we report on a straightforward high-pressure synthesis procedure and a profound investigation on the crystallographic structure by both neutron and X-ray diffraction techniques, X-ray photoelectron spectroscopy (XPS) analysis, magnetic and magnetocaloric properties of some members of the…”

“…Particularly, the high-pressure methods to synthesize new compounds have some advantages over the conventional ambient pressure methods, including stabilization of metastable phases with unusual valence states and enhanced densification. 26 In this paper, we report on a straightforward high-pressure synthesis procedure and a profound investigation of the crystallographic structure by both neutron and X-ray diffraction techniques. We have performed an X-ray photoelectron spectroscopy (XPS) analysis, and also the magnetic and magnetocaloric properties of some members of the Fe x Ti 2 S 4 Heideite family are determined, showing some appealing results concerning MCE for some compositions.…”

Evidence for a Pressure-Induced Phase Transition in the Highly Distorted TlNiO3 Nickelate

“…Recently, synthesis approaches based on high-pressure methods have allowed producing pure and highly crystallized nickelates in sufficient quantities for the characterization of their structural, electronic, and transport properties. 21 TlNiO 3 , belonging to the group of the small R cation nickelates, represents a very interesting candidate to probe the mechanism of the IMT. In contrast to the rare-earth cations, Tl 3+ in TlNiO 3 has fully filled 4f orbitals, which is a unique electronic configuration of an A-site cation in nickelates.…”

SnSe:Kx intermetallic thermoelectric polycrystals prepared by arc-melting

“…Skutterudites are another attractive family of thermoelectrics, as they are high mobility semiconductors that chemically and structurally offer many ways of doping and property tuning [1, 32,33]. They can be prepared by various methods in addition to conventional metallurgy, including high-pressure synthesis [34][35][36], melt spinning [37,38], microwave synthesis [39], etc. As alternatives, oxides, such as SrTiO 3 have been considered recently [40,41].…”