Pressure transition of AlP to a conductive phase

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Abstract
Van Vechten, using a semi-empirical theoretical approach, has computed the equilibrium pressures at which various III-V compounds as well as C, Si, Ge, Sn, and SiC transform to the metallic β-tin phase. A characteristic of each of the groups BX, AlX, GaX, and InX, where X is a specific metalloid (N, P, As, Sb), is that the theoretical transformation pressure decreases as the atomic number of the metal atom B, Al, Ga, and In increases. The calculated values for the sequence BP, AlP, GaP, and InP are 401, 269, 216, and 141 kbar, respectively. Currently published values are available for GaP at 220 and 240 kbar and for InP at 105–115 kbar. In the present experiment, in which a direct simultaneous electric resistance comparison method is used, it is shown that AlP becomes conductive at a pressure equal to or less than ZnS which has been shown to transform at 150 kbar. Note should be made of the fact that the pressure at which we find AlP to be conductive is clearly considerably less (rather than more) than the pressure at which GaP becomes conductive. Direct simultaneous comparison with GaP in our cell also shows this to be the case. The possibility is suggested that the conductive phase of AlP seen here may not have the β-tin structure for which Van Vechten’s calculations apply, but instead may have the sodium chloride structure for which his calculations do not apply.