High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations

Abstract

The high-pressure structural behavior of the binary intermetallic compounds CoSn, FeSn, and NiIn with the peculiar void containing CoSn ͑B35͒-type structure has been studied by means of room-temperature diamond anvil cell and high-temperature multianvil experiments, as well as by first-principles calculations. All three compounds remain structurally stable at pressures up to at least 25 GPa, whereas first-principles calculations predict high-pressure structural changes below 20 GPa. A plausible explanation for the discrepancy is that at room temperature, a sizable activation barrier inhibits kinetically the transformation into more close-packed polymorphs. It is supported by our experiments at temperatures around 1000°C and a pressure of 10 GPa. At these conditions, NiIn transforms into the temperature-quenchable stoichiometric CsCl-type high-pressure phase, which has been predicted in our first-principles calculations. However, CoSn and FeSn decompose into a mixture of compounds richer and poorer in tin, respectively. Nevertheless, it might be possible that lower temperatures and higher pressures may afford theoretically predicted polymorphs. In particular, a phase transformation to the FeSi-type structure predicted for CoSn is of interest as materials with the FeSi-type structure are known for unusual thermal and transport properties.

Ordered CoSn-type ternary phases in Co3Sn3−xGex

“…While this does not preclude the possibility of a distorted high-pressure phase that can relax back to the ambient form, the lack of decomposition products does prove that this material is stable with respect to the simple binaries under these conditions. CoSn reportedly decomposes upon heating to 1000°C at extreme pressures (26 GPa) [11] that we are unable to reach, so we cannot compare the relative stabilities of the two phases under those conditions Fig. 5 shows the temperature dependent magnetic susceptibility for x = 0, 1, and 2, that is for CoSn, Co 3 Sn 2 Ge, and Co 3 SnGe 2 .…”

“…Calculations suggest that the structure should transform under high pressure to either the FeSi or CoGe structure types, and then finally to the cubic CsCl structure [11,12]. However, experimentally it is found that CoSn maintains its structure up to at least 38 GPa at ambient temperature, though heating under pressure causes it to dissociate into a combination of CoSn 2 and Co 3 Sn 2 [11,13]. It has been suggested that this unusual stability in spite of the small packing fraction arises from occupation of the void either by stereochemically active electrons from Sn [13] or a small amount of undetectable hydrogen [14].…”

“…These have been of interest recently because the void in the honeycomb layer yields a structure with an anomalously small packing fraction (55%) [11], implying that it should be unstable with respect to pressure. Calculations suggest that the structure should transform under high pressure to either the FeSi or CoGe structure types, and then finally to the cubic CsCl structure [11,12].…”

“…These have been of interest recently because the void in the honeycomb layer yields a structure with an anomalously small packing fraction (55%) [11], implying that it should be unstable with respect to pressure. Calculations suggest that the structure should transform under high pressure to either the FeSi or CoGe structure types, and then finally to the cubic CsCl structure [11,12]. However, experimentally it is found that CoSn maintains its structure up to at least 38 GPa at ambient temperature, though heating under pressure causes it to dissociate into a combination of CoSn 2 and Co 3 Sn 2 [11,13].…”

FP-(L)APW + lo study of mechanical stability and electronic behavior of CoGe in B20 structure

“…These areas include the biological impact of electromagnetic emission, electromagnetic interference, energy conservation and emission as well as public health, especially prevention of hazards caused by electromagnetic emission systems [6]. Certain B20 often display interesting magnetic, thermal and transport properties despite the fact that the possibility of their corresponding phase transformation is problematic [7][8][9].…”