Metal to Semimetal Transition in CaMgSi Crystals Grown from Mg−Al Flux

Abstract

Single crystals of CaMgSi were produced using the metal flux synthesis method in a Mg/Al 1:1 mixture. The large rod-shaped crystals measure up to 7 mm in length. This phase crystallizes with the orthorhombic TiNiSi structure type (space group Pnma; a = 7.4752(2) Å, b = 4.42720(10) Å, c = 8.3149(2) Å; R 1 = 0.021). Despite its relationship to semiconducting Zintl phases Mg2Si and Ca2Si, CaMgSi is metallic at room temperature; this produces a positive (∼160 ppm) 29Si MAS NMR chemical shift and is supported by DOS calculations. A metal to semimetal electronic transition at around 50 K is evident in the resistivity, magnetic susceptibility, and electron paramagnetic resonance measurements. Low temperature powder X-ray diffraction data indicates that a structural distortion accompanies this transition. The electronic heat capacity coefficient (0.4695 mJ/mol·K2) determined from low temperature heat capacity data supports the designation of CaMgSi as a semimetal at low temperature. The hydrogen storage capacity of this phase is negligible (≤0.5 wt % hydrogen), although exposure to hydrogen does destabilize the structure, inducing decomposition at 500 °C.

Energetic prediction of Mg2Si–Ca2Si pseudobinary system using first-principles calculations

“…Therefore, CaMgSi is predicted to be a semimetal, although both Mg 2 Si and Ca 2 Si are known semiconductors. This prediction is consistent with the observed temperature dependence of the resistivity above 50 K [19].…”

Different Topological Quantum States in Ternary Zintl compounds: BaCaX (X = Si, Ge, Sn and Pb)

“…The choice of PBE with experimental lattice parameters is justified by the very good agreement between PBE band structures and angle-resolved photo-electron spectroscopy (ARPES) experiments for many topological semimetals. Specifically, for the related silicide compound CaMgSi, PBE band structures predict a semimetal and was confirmed in single crystal transport experiment 75 .…”

Applications of nuclear shielding

“…(B160 ppm) 29 Si MAS NMR chemical shift. 250 A series of N-heterocyclic carbene-stabilised silanechalcogenones 2a,b (Si = O), 3a,b (Si = S), 4a,b (Si = Se) and 5a,b (Si = Te) were described. These novel compounds were isolated in a crystalline form in high yields and were characterised by multinuclear NMR spectroscopy.…”