4 research outputs found
Synthesis and Structure of Two New Cadmium Carbonates at Extreme Conditions
We
synthesized CdC2O5 and a new high-pressure
polymorph of CdCO3 by laser heating otavite, CdCO3, in CO2 at 43 GPa. The structure of CdC2O5 contains pyramidal [C4O10]4ā building blocks formed by [CO4] tetrahedra, where the
carbon is in 4-fold coordination. In addition, we found a new monoclinic
(P21/c) high-pressure
polymorph of CdCO3 with trigonal [CO3]2ā groups. Both new structures were characterized by single-crystal
X-ray diffraction, Raman spectroscopy, and DFT calculations
High-Pressure Synthesis of Ī²āIr<sub>4</sub>B<sub>5</sub> and Determination of the Compressibility of Various Iridium Borides
A new
iridium boride, Ī²-Ir<sub>4</sub>B<sub>5</sub>, was
synthesized under high-pressure/high-temperature conditions of 10.5
GPa and 1500 Ā°C in a multianvil press with a Walker-type module.
The new modification Ī²-Ir<sub>4</sub>B<sub>5</sub> crystallizes
in a new structure type in the orthorhombic space group <i>Pnma</i> (no. 62) with the lattice parameters <i>a</i> = 10.772(2)
Ć
, <i>b</i> = 2.844(1) Ć
, and <i>c</i> = 6.052(2) Ć
with <i>R</i>1 = 0.0286, <i>wR</i>2 = 0.0642 (all data), and <i>Z</i> = 2. The structure
was determined by single-crystal X-ray and neutron powder diffraction
on samples enriched in <sup>11</sup>B. The compound is built up by
an alternating stacking of boron and iridium layers with the sequence
ABAā²Bā². Additionally, microcalorimetry, hardness, and
compressibility measurements of the binary iridium borides Ī±-Ir<sub>4</sub>B<sub>5</sub>, Ī²-Ir<sub>4</sub>B<sub>5</sub>, Ir<sub>5</sub>B<sub>4</sub>, hexagonal Ir<sub>4</sub>B<sub>3ā<i>x</i></sub> and orthorhombic Ir<sub>4</sub>B<sub>3ā<i>x</i></sub> were carried out and theoretical investigations
based on density function theory (DFT) were employed to complement
a comprehensive evaluation of structureāproperty relations.
The incorporation of boron into the structures does not enhance the
compressibility but leads to a significant reduction of the bulk moduli
and elastic constants in comparison to elemental iridium
Materials Properties of Ultra-Incompressible Re<sub>2</sub>P
In situ high-pressure X-ray powder diffraction measurements
on
Re<sub>2</sub>P up to 37.0 GPa at ambient temperature in diamond-anvil
cells were carried out at two different synchrotron facilities (ESRF
and DESY). The compressibility of Re<sub>2</sub>P (<i>Pnma</i>, no. 62, <i>a</i> = 5.5464(17), <i>b</i> = 2.9421(8), <i>c</i> = 10.0483(35) Ć
, <i>V</i> = 163.97(9) Ć
<sup>3</sup>, <i>Z</i> = 4, <i>R</i><sub>p</sub> = 0.1008, <i>wR</i><sub>p</sub> =
0.1341 at ambient conditions) was investigated and resulted in a bulk
modulus of <i>B</i><sub>0</sub> = 320(10) GPa after fitting the experimental <i>p</i>ā<i>V</i> data to a second- and third-order BirchāMurnaghan
equation of state. In addition, the determined bulk modulus is compared
to values obtained from an Eulerian strain versus normalized stress
plot with values ranging form 315(7) to 321(15) GPa. These experimental
findings are confirmed by density functional theory (DFT)-calculations
ranking Re<sub>2</sub>P among ultra-incompressible materials. However,
the Vickers hardness of a high-pressure sintered Re<sub>2</sub>PāRe<sub><i>x</i></sub>C<sub><i>y</i></sub> composite
material in the asymptotic hardness region was found to be of only
13(2) GPa. Electrical conductivity measurements indicate that metallic
Re<sub>2</sub>P exhibits Pauli-paramagnetism. Analysis of temperature-dependent
in situ X-ray diffractometry reveals an approximately isotropic expansion
of the lattice parameters with a thermal expansion coefficient of
(Ī±Ā(<i>V</i>) = 28.5ā32.8(2)Ā·10<sup>ā6</sup> K<sup>ā1</sup>)
Determination of the Crystal Structure of Hexaphenyldisilane from Powder Diffraction Data and Its Thermodynamic Properties
The crystal structure of hexaphenyldisilane,
Si<sub>2</sub>(C<sub>6</sub>H<sub>5</sub>)<sub>6</sub>, was determined
from synchrotron
powder diffraction data. The compound crystallizes in orthorhombic
space group <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub> with the following unit cell dimensions: <i>a</i> = 20.2889(8)
Ć
, <i>b</i> = 16.9602(7) Ć
, and <i>c</i> = 8.5506(4) Ć
. Second-harmonic generation measurements as well
as density functional theory calculations were used to confirm the
structure determination. The combination of experimental and theoretical
studies yields a SiāSi distance [<i>d</i>(SiāSi)]
of 2.38 Ć
. The phenyl rings of a molecule are staggered and slightly
distorted, so that the molecule is acentric. Thermodynamic measurements
showed no phase transition in the temperature range of 2ā400
K. The molar heat capacity (<i>C<sub>p</sub></i>) at 298.15
K of 604(6) J mol<sup>ā1</sup> K<sup>ā1</sup> was established
experimentally and by lattice dynamic calculations. The molar entropy
(<i>S</i>Ā°) and the molar enthalpy (Ī<i>H</i>) in the temperature range of 0ā298.15 K are 674(7)
J mol<sup>ā1</sup> K<sup>ā1</sup> and 97(6) kJ mol<sup>ā1</sup> respectiveley. The Debye temperature (Īø<sub>D</sub>) is 207(5) K. The thermal expansion of Si<sub>2</sub>(C<sub>6</sub>H<sub>5</sub>)<sub>6</sub> is strongly anisotropic, and negative
in two directions as determined via temperature-dependent X-ray powder
diffraction experiments. The linear thermal expansion coefficients
at 298.15 K are as follows: Ī±<sub><i>a</i></sub> =
ā4(2) Ć 10<sup>ā6</sup> K<sup>ā1</sup>,
Ī±<sub><i>b</i></sub> = ā4(2) Ć 10<sup>ā6</sup> K<sup>ā1</sup>, and Ī±<sub><i>c</i></sub> = 2.21(4) Ć 10<sup>ā4</sup> K<sup>ā1</sup>. The volumetric thermal expansion coefficient (Ī±<sub><i>V</i></sub>) at 298.15 K is 2.13(5) Ć 10<sup>ā4</sup> K<sup>ā1</sup>