Thermal, Crystallographic, and Mechanical Properties

Earlier investigations of the physical properties of phosphane are described in Phosphor C, 1965, pp. 24/30 thermodynamic data of formation are given on pp. 10/1 and solubility data on p. 50 of that volume. 

Phase Transition. Temperatures. The boiling point of PH3 at normal pressure, 185.5 K, was extrapolated from vapor pressure measurements see Phosphor C, 1965, p. 26. PD3 boils at 188 K [1]. The other phase transitions of PH3 under its own pressure were identified by measuring the heat capacity. Liquid PH3 (and PD3 [1]) solidifies at the triple point temperature of 139.4 K, forming the plastic crystalline phase a. Cooling to 88.3 K results in conversion to the crystalline phase p. The conversion of the p phase to the stable crystalline phase y requires several days and has a transition temperature of 49.4 K. The temperature for the fast transition between the p phase and the metastable crystalline 6 phase is 30.3 K details are described in Phosphor C, 1965, pp. 24,29. An IR investigation showed the conversion of the 8 phase into the more stable y phase to be an extremely slow process [2]. 

The phase transition of PH3 and PD3 were investigated more recently by vibrational spectroscopy of crystalline films. The resulting transition temperatures in K are as follows [3]  

The p Y phase transition of PD3 was found to proceed in the temperature range 50 to 60 K with a hysteresis typical for a first-order transition. The low-temperature y phase was stable down to 6 K [4]. The p- y conversion is quite fast for PD3 in contrast to that of PH3 [3] as described in the preceeding paragraph. The temperature for the transition of PD3 between the crystalline phase p and the plastic crystalline phase a of 93.5 K is significantly higher than the corresponding temperature of 88.2 K for PH3 [5]. 

Indications of an additional phase transition of PH3 at 10 K [6] were found to be erroneous [2. 3]. 

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