Phonon optics, thermal expansion tensor, thermodynamic and chemical bonding properties of Al4SiC4 and Al4Si2C5: a first-principles study

RSC Advances ◽  
2016 ◽  
Vol 6 (49) ◽  
pp. 43191-43204 ◽  
Author(s):  
Y. F. Li ◽  
B. Xiao ◽  
L. Sun ◽  
Y. M. Gao ◽  
Y. H. Cheng
Keyword(s):  
Crystal Structure ◽  
Thermal Expansion ◽  
Chemical Bonding ◽  
First Principles ◽  
Phonon Mode ◽  
Side View ◽  
Negative Mode ◽  
Thermal Expansion Tensor ◽  
Bonding Properties ◽  
Grüneisen Constant

The creation of stacking fault in Al4SiC4 crystal structure due to a phonon mode (E1, 139.7 cm−1, Raman active) at Γ-point with negative mode-Grüneisen constant (−0.28). (a) 3-D side-view; (b) 2-D side view.

A high temperature structural phase transition in crocoite (PbCrO4) at 1068 K: crystal structure refinement at 1073 K and thermal expansion tensor determination at 1000 K

2000 ◽  
Vol 64 (2) ◽  
pp. 291-300 ◽  
Author(s):  
K. S. Knight
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Thermal Expansion ◽  
High Temperature ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Structure Type ◽  
Temperature Phase ◽  
Thermal Expansion Tensor ◽  
Principal Axes

AbstractHigh-resolution, neutron time-of-flight, powder diffraction data have been collected on natural crocoite between 873 and 1073 K. Thermal analysis carried out in the 1920s had suggested that chemically pure PbCrO4 exhibited two structural phase transitions, at 964 K, to the β phase, and at 1056 K, to the γ phase. In this study, no evidence was found for the α-β structural phase transition, however a high-temperature phase transition was found at ∼1068 K from the ambient-temperature monazite structure type to the baryte structure type. The phase transition, close to the temperatures reported for the β to γ phase modifications, is first order and is accompanied by a change in volume of −1.6%. The crystal structure of this phase has been refined using the Rietveld method to agreement factors of Rp = 0.018, Rwp = 0.019, Rp = 0.011. No evidence for premonitory behaviour was found in the temperature dependence of the monoclinic lattice constants rom 873 K to 1063 K and these have been used to determine the thermal expansion tensor of crocoite just below the phase transition. At 1000 K the magnitudes of the tensor coefficients are α11, 2.66(1) × 10−5 K−1; α22, 2.04(1) × 10−5 K−1; α33, 4.67(4) × 10−5 K−1; and α13, −1.80(2) × 10−5 K−1 using the IRE convention for the orientation of the tensor basis. The orientation of the principal axes of the thermal expansion tensor are very close to those reported previously for the temperature range 50–300 K.

First-principles investigations of the electronic, optical and chemical bonding properties of SnO2

1997 ◽  
Vol 7 (12) ◽  
pp. 2547-2550 ◽  
Author(s):  
Ph. Barbarat ◽  
S. F. Matar ◽  
G. Le Blevennec
Keyword(s):  
Chemical Bonding ◽  
First Principles ◽  
Bonding Properties

Synthesis and structural characterization of BaV4O9

2007 ◽  
Vol 63 (2) ◽  
pp. 270-276 ◽  
Author(s):  
Thomas Reeswinkel ◽  
Sebastian Prinz ◽  
Karine M. Sparta ◽  
Georg Roth
Keyword(s):  
Crystal Structure ◽  
Thermal Expansion ◽  
Structural Characterization ◽  
Room Temperature ◽  
Monoclinic Space Group ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Expansion Tensor

The new spin ½ V4+ barium oxovanadate BaV4O9 was synthesized and studied by means of single-crystal X-ray diffraction. Its room-temperature structure is monoclinic, space group P2/c. We discuss the temperature evolution of the crystal structure and thermal expansion tensor of the material between 293 and 100 K.

Structural, Electronic and Optical Properties of High (γ)-Li2BeSiO4: First-Principles Calculations

2011 ◽  
Vol 197-198 ◽  
pp. 567-570
Author(s):  
Qi Jun Liu ◽  
Zheng Tang Liu ◽  
Li Ping Feng ◽  
Hao Tian
Keyword(s):  
Optical Properties ◽  
Chemical Bonding ◽  
First Principles ◽  
Density Functional ◽  
Structural Parameters ◽  
Population Analysis ◽  
Functional Theory ◽  
Charge Densities ◽  
Bonding Properties ◽  
Direct Band

We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, electronic structure, chemical bonding and optical properties of orthorhombic Li2BeSiO4. The calculated lattice parameters are in agreement with experimental data. The band structure shows a direct band gap. From the DOS analysis, charge densities and population analysis, electronic and chemical bonding properties have been studied. Furthermore, in order to understand the mechanism of optical transitions of orthorhombic Li2BeSiO4, the complex dielectric functions are calculated and analysed.

Structural and thermal properties of the monoclinic Lu2SiO5single crystal: evaluation as a new laser matrix

2009 ◽  
Vol 42 (2) ◽  
pp. 284-294 ◽  
Author(s):  
Hengjiang Cong ◽  
Huaijin Zhang ◽  
Jiyang Wang ◽  
Wentao Yu ◽  
Jiandong Fan ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Specific Heat ◽  
Linear Thermal Expansion ◽  
Cell Parameters ◽  
Thermal Expansion Tensor ◽  
Anisotropic Thermal Conductivity

The crystal structure of monoclinic Lu2SiO5(LSO) crystals, grown by the Czochralski method, was determined at room temperature by X-ray diffraction. The unit-cell parameters area= 10.2550 (2),b= 6.6465 (2),c= 12.3626 (4) Å, β = 102.422 (1)° in space groupI2/a. The linear thermal expansion tensor was determined along thea,b,candc* directions over the temperature range from 303.15 to 768.15 K, and the principal coefficients of the thermal expansion tensor are found to be αI= −1.0235 × 10−6 K, αII= 4.9119 × 10−6 K and αIII= 10.1105 × 10−6 K. The temperature dependence of the cell volume and monoclinic angle were also evaluated. In addition, the specific heat and the thermal diffusivity were measured over the temperature ranges from 293.15 to 673.15 K and from 303.15 to 572.45 K, respectively. As a result, the anisotropic thermal conductivity could be calculated and is reported for the first time, to the best of the authors' knowledge. The specific heat capacity of LSO is 139.54 J mol−1 K−1, and the principal components of the thermal conductivity arekI= 2.26 W m−1 K−1,kII= 3.14 W m−1 K−1andkII= 3.67 W m−1 K−1at 303.15 K. A new structure model was proposed to better understand the relationships between the crystal structure and anisotropic thermal properties. In comparison with other laser matrix crystals, it is found that LSO possesses relatively large anisotropic thermal properties, and owing to its small heat capacity it has a moderate thermal conductivity, which is similar to those of the tungstates but lower than those of the vanadates.

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