F. A. Mauer

Raman and x‐ray investigations of ice VII to 36.0 GPa

Raman data for ice VII to 30 GPa and x‐ray lattice parameters to 36 GPa, all at room temperature, are presented and discussed. Both the Raman OH‐stretching peak frequency (Δv) and the edge distance of the body‐centered cubic unit cell (a) decrease at a decreasing rate with pressure rise. The OH peak frequency is found to be virtually linear in the nearest‐neighbor O–O distance (rOO) between about 2.5 and 2.9 A. However, the data can also be fitted with a slight cubic dependence, which when extrapolated, gives rise to a minimum in Δv at rOO=2.35±0.06 A. This is close to the value of 2.4 A found for the symmetric O–H–O units in other materials. This minimum suggests, but does not prove, that a symmetric hydrogen bond structure O–H–O, and thus a new ice, may result at pressures of about 75±20 GPa. Treatment of the O–H⋅⋅⋅O units according to couplet oscillators using experimentally confirmed assumptions indicates that Δv≊A/rOH2 which when combined with present and previously published data yields, approxim...

Isothermal equations of state for H2O‐VII and D2O‐VII

Lattice parameters and cell volumes at room temperature are reported for H2O‐VII to 36 GPa and for D2O‐VII to 32 GPa. The data are fitted to seven isothermal equations of state from which are derived averaged values of the isothermal bulk moduli (B) and their pressure derivatives (dB/dP) as a function of pressure. For H2O over the range 2.33⩽P⩽30.9 GPa, B increases from 22.3 to 141.0 GPa while dB/dP decreases from 4.9 to 3.7. For D2O over the range 2.8⩽P⩽30.27 GPa, B increases from 30.0 to 129.0 GPa while dB/dP decreases from 4.1 to 3.1. An independent determination of B and dB/dP using a piecewise regression analysis gives B = 15.78+4.11 P, GPa with no distinction between H2O and D2O over the observed pressure ranges. The procedures employed for treating the data and the reliability of the derived results are assessed for both materials.

Phase transition and compression of LiNbO3 under static high pressure

Lattice parameters of LiNbO3 were measured at room temperature over the pressure range 0–35 GPa by x‐ray diffraction using the diamond anvil cell. In the region below 13 GPa (where a hydrostatic pressure was maintained) the pressure dependence of the volume can be well described by the Birch–Murnaghan equation of state, yielding B0=134±3 GPa for the zero‐pressure bulk modulus and B’0 =2.9±0.5 for its pressure derivative. A phase transformation was detected at 30±3 GPa both by x‐ray diffraction and by optical observation of the change from a transparent to an opaque state. The pattern of the high‐pressure phase was tentatively indexed on the basis of a cubic cell with a=6.78 A.

Thermal expansion and low temperature phase transition of thallous azide

Thallous azide, TIN3, is tetragonal at room temperature. It transforms at 248 ± 5 °K to a phase that can be indexed on the basis of an orthorhombic cell. Lattice parameters of the tetragonal phase have been determined by the Bond single crystal method at intervals of approximately 25 °K from 248 to 498 °K. Single crystals do not survive the transition, so the parameters of the orthorhombic phase were measured by powder diffraction at intervals of 25 °K down to 133 °K. Representative parameters, after corrections for the effects of radiation damage, are a = 6.2094 A, c = 7.3583 A at 298.2 °K for the tetragonal phase, and a = 8.718 A, b = 8.766 A, c = 7.395 A at 238.2 °K for the orthorhombic. Thermal expansion parameters show anomalies that are believed to be the result of changes in the orientation of azide ions. The linear expansion coefficients, αa and αc, for the tetragonal phase are both approximately 5.2 × 10−5 °K−1 at the transition. By 486 °K, αc has increased to 21 × 10−5 °K−1 and αa has decreased ...

Temperature distribution in the diamond anvil pressure cell at high temperature

The temperature distribution in a diamond anvil pressure cell is investigated theoretically for a model cell having a cylindrical external heater. For a heater surface at 1000 absolute degrees above the ambient temperature, it is found, at steady state, that the region of the sample chamber is, for all practical purposes, isothermal at a temperature of about 11 degrees below the temperature of the heater. When the heater temperature is subsequently incremented instantaneously by 10 degrees, a new steady state is reached in about 30 sec.

Crystal and Molecular Structure of C4B20H22, Bis (o‐dodecacarborane)

The molecular configuration of bis(o‐dodecacarborane), C4B20H22, has been determined in a complete three‐dimensional x‐ray crystallographic study. It is demonstrated that the C2B10 unit in each half of the molecule corresponds to a slightly distorted icosahedron. The two halves of the molecule are joined by a carbon—carbon single bond (1.522 A) and are related by a center of symmetry. The unit cell is monoclinic with a=7.014±0.001 A, b=9.862±0.001 A, c=12.360±0.002 A, and β=90°31′±2′. Z=2 and the space group is P21/n. The R value for 1899 reflections is 6.8% and for the 1749 observed reflections it is 6.4%.

Compression studies of a nickel‐based superalloy, MAR‐M200, and of Ni3Al

The lattice parameter of a cubic nickel‐based alloy, MAR‐M200, has been determined as a function of pressure for 0<p<14 GPa at room temperature. A similar study was made for Ni3Al in the range 0<p<11 GPa at room temperature. In both cases, the diamond anvil pressure cell was used in conjunction with the energy dispersive method of x‐ray diffraction. The data were analyzed in the context of model equations of state and in comparison with other results from ultrasonic studies.

Exploratory Study, by Low‐Temperature X‐Ray Diffraction Techniques, of Diborane and the Products of a Microwave Discharge in Diborane

It has been suggested that atomic hydrogen may form a loose, one‐electron bond with stable electron‐deficient molecules such as diborane (B2H6). Such bonding might make possible the stabilization of quasi‐atomic hydrogen at higher temperatures or in higher concentrations than have been attained previously. To test this theory, diborane and the products of a microwave discharge in diborane have been studied by x‐ray diffraction in the temperature range 4.2° to 100°K.Two structurally related phases have been distinguished in ordinary diborane. The low temperature or α phase is formed by deposition from the gas at 4.2°K. It transforms slowly to β diborane above 60°K. The β phase is also obtained by depositing at 77°K and annealing above 90°K to eliminate traces of the α phase.An additional phase is found in specimens formed by freezing at 4.2°K the products of a microwave discharge in diborane. It is probably a boron‐hydrogen compound with a triple‐point temperature of about 60°K. It may be BH3. This compoun...

Diamond Anvil Cell Technology For P,T Studies Of Ceramics: ZrO2 (8 mol% Y2O3)

We are undertaking a systematic study of the structural and bulk properties of zirconia and other ceramic materials as functions of pressure and temperature. This paper describes the experimental approach that is being taken and discusses some of the results already obtained for ZrO2 with 8 mol% Y2O3.

Radial distribution studies of amorphous Fe–W and Ni–P at high pressure

The procedure for the determination of a radial distribution function of an amorphous material contained in a diamond anvil pressure cell is discussed. The details of the method of computation are presented, and the results for two amorphous metals, Fe–W (72 at. % Fe) and Ni–P (75 at. % Ni), are presented and critically discussed. For the reduced structure function and its Fourier transform, the differential radial distribution function, amplitudes are not well determined, and maxima and minima are located with an absolute accuracy not better than 3%. However, for a single experimental configuration and sample, the relative changes in the first neighbor distance as a function of pressure are readily detectable, even for variations on the order of 0.5%. Measurements at 0, 0.3, 3.6, 7.5, and 10.5 GPa and room temperature indicate that Fe–W (72 at. % Fe) has a bulk modulus of about 170 GPa and has a volume compression of about 6% at 10.5 GPa. Measurements at 0.15, 2.80, and 5.50 GPa indicate that Ni–P (75 at...