P.W. Richter

High-pressure phase relations of RbH2PO4, CsH2PO4, and KD2PO4

Abstract The phase diagrams of RbH2PO4 (RDP), CsH2PO4 (CDP), and KD2PO4 (DKDP) have been determined to ∼40 kbar. Attempts are made to correlate the present phase diagrams with that of KH2PO4 and determine which phases are isostructural. The large isotope effect found for KD2PO4 is in agreement with the isotope effects in H2O, D2O.

Phase diagrams to 40 kbar and crystallographic data for RbNO2 and CsNO2

Abstract CsNO2 I at ambient conditions is cubic, space group Oh1-Pm3m, with a0 = 4.389A, and transforms at −94°C to rhombohedral CsNO2 II, space group D 5 3d -R 3 m , with arh = 4.307A, α = 87°22′. The CsNO2 II I transition line rises with pressure. RbNO2 I at ambient conditions is cubic, space group Oh5-Fm3m, with a0 = 6.934A. It transforms at −12°C to monoclinic RbNO2 II with a0 = 8.904, b0 = 4.828, c0 = 8.185A, β = 115.7° at −62°C. RbNO2 II appears to be ordered, whereas RbNO2 I has a configurational entropy of Rln32. The RbNO2 II I transition line is terminated at 0.3 kbar with the appearance of RbNO2 III which is 17.3% denser than RbNO2 I. The RbNO2 II III transition pressure increases with decreasing temperature to a triple point at 1.2 kbar, −65°C where a further dense phase RbNO2 IV appears. The RbNO2 IV III phase boundary is very similar to the CsNO2 II I boundary. The RbNO2 II IV transition pressure rises slightly with decreasing pressure. The melting curve of RbNO2 I passes through a maximum at 2.2 kbar, 390°C, and is terminated at the RbNO2 III/I/liquid triple point at 5.2 kbar, 382°C. The melting curve of RbNO2 III rises steeply with pressure.

Phase relations of CsClO4 and CsBF4 to high pressures

Orthorhombic CsBF4 III transforms at 159.1°C to cubic CsBF4 II, space group Fm3m, with a0 = 7.859 A at 230°C. The high-pressure phase diagrams of CsClO4 and CsBF4 were studied by means of differential thermal analysis and volumetric techniques, and found to be closely similar to those of RbClO4 and RbBF4. All the new phases previously predicted for CsBF4 actually appeared. Entropy calculations confirmed the earlier suggestion that the entropy change of the RbBF4 I/IV, CsClO4 II/I and CsBF4 II/I transitions approximately equals Rln 8.

High-pressure synthesis of YScO3, HoScO3, ErScO3, and TmScO3, and a reevaluation of the lattice constants of the rare earth scandates

The rare earth scandates AScO/sub 3/, where A = Y, La, Nd, Sm, Gd, Dy, Ho, Er, and Tm, were prepared, and their unit cell constants were determined. The single-phase compounds YScO/sub 3/, HoScO/sub 3/, ErScO/sub 3/, and TmScO/sub 3/ were prepared for the first time by use of high pressures. 1 figure, 4 tables.

Binary alloy systems at high pressure

Abstract The composition-temperature-pressure phase relations of binary alloy systems are discussed. Topics include the effect of pressure on liquidi and eutectic points, the effect of pressure on solid solubility, polymorphism of intermetallic compounds, the formation and dissociation of intermetallic compounds, the similarity of phase diagrams of related systems and the coupling of composition-temperature-pressure phase diagrams with thermochemical data. The systems HgTl, AlSi, AlGe, ZnAs and CdPb are presented as examples.

The infrared spectra, phase transition, and structural properties of tetraethylammonium hexafluoroantimonate (C2H5)4NSbF6

Abstract (C2H5)4NSbF6 (TEAHFA) is face-centered cubic with a = 11.487 A at ambient temperature and undergoes a first-order phase transition at 246 K on cooling and at 272 K on heating. The infrared spectra of TEAHFA confirm the cubic structure of the room temperature phase I in which no evidence could be found for the existence of hydrogen bonds between the cations and anions.

High-pressure/high-temperature phase relations and vibrational spectra of CsSbF6

CsSbF6(II) under ambient conditions is trigonal, space group D3d5-R3m. At 187.8°C it undergoes a phase transition with an enthalpy change of 5.267 ± 0.316 kJ mole−1, to phase CsSbF6(I). CsSbF6 decomposes with loss of fluorine at atmospheric pressure at high temperatures, but under pressure the decomposition is prevented and a melting point of 310°C at atmospheric pressure can be inferred. The III phase boundary and melting curve were studied as functions of pressure. The infrared and Raman spectra of CsSbF6(II) were studied in the temperature range of −256 to 20°C, at ambient pressure. The crystal chemistry of the CsSbF6 and its relationship with other related compounds is discussed.

Effect of Pressure on the Phase Relations of Some n-Paraffins

Abstract The phase diagrams of n-C21H44, n-C25H52, n-C22H46, n-C24H50 and n-C32H66 were studied to 40 kbar by means of differential thermal analysis and volumetric techniques. n-C21H44 and n-C25H52 have orthorhombic/hexagonal/liquid triple points near 3 kbar, with the triple points marked by definite inflections in the melting curves. n-C22H46 transforms to a suspected monoclinic phase at ∼2.6 kbar, 22°C. It is concluded that even nparaffins below n-C22H46 will all have similar high-pressure transformations. n-C24H50 has the triclinic/monoclinic transition at ∼44°C, 1 bar. The high-pressure melting curves of the even n-paraffins studied here all refer to the monoclinic phases, and are remarkably similar in slope and curvature, but have considerably less curvature than the orthorhombic odd n-paraffins. The monoclinic (or triclinic)/hexagonal/liquid triple points of the even n-paraffins studied are located at or below 1 kbar. The usual monoclinic phase of even n-paraffins above ∼n-C26H54 is a high-pressure ...

Phase relations of NH4ClO4 and NH4BF4 to high pressures

Abstract The high pressure phase diagrams of NH 4 ClO 4 and NH 4 BF 4 were studied by means of differential thermal analysis and volumetric techniques. The high temperature portions of these diagrams are intermediate between those of the corresponding potassium and rubidium salts, but at low temperatures the onset of hydrogen bonding causes the appearance of phases which are unique to the ammonium compounds.

Effect of pressure on the melting point of Hg5Tl2

Abstract The melting point of Hg 5 Tl 2 rises with pressure with a slope of 3.44°/kbar. No curvature of the melting curve was evident up to ~ 35 kbar. Hg 5 Tl 2 melts at a higher temperature than Hg in this pressure region, but although the initial slope of the melting curve of Hg is considerably higher than for Hg 5 Tl 2 , the slopes are closely similar near ~ 35 kbar. The two melting curves can be expected to remain within a few degrees to ~ 60 kbar. No evidence of the disproportionation of Hg 5 Tl 2 was observed in the pressure range studied.