scholarly journals Rationalization of Lattice Thermal Expansion for Beta-Blocker Organic Crystals

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 350
Author(s):  
Paola Paoli ◽  
Stella Milazzo ◽  
Patrizia Rossi ◽  
Andrea Ienco
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Harmonic Approximation ◽  
Complete Analysis ◽  
Lattice Expansion ◽  
Primary Role ◽  
Organic Crystals ◽  
Hydrogen Bond System ◽  
Anisotropic Lattice ◽  
Β Blocker

Anisotropic lattice expansion could be a source of misunderstanding in powder pattern recognitions, especially in the case of organic crystals where for the interpretation of room temperature patterns single crystal data at low temperature are usually used. Trying to rationalize the thermal lattice expansion, we studied two close related β-blocker molecules with similar packing in the solid state but with different thermal behavior. Solid state calculations, using the fast and accurate HF-3c method and the quasi harmonic approximation for the simulation of the lattice expansion, were able to reproduce the experimental trends with good accuracy. The complete analysis of the calculated thermal expansion of the two structures, as well as of other structures with similar packing found in a database survey, revealed the primary role of the hydrogen bonds. Secondary non-covalent interactions in the plane perpendicular to the hydrogen bond system could also play a role.

scholarly journals Electronic Property and Negative Thermal Expansion Behavior of Si136-xGex (x = 8, 32, 40, 104) Clathrate Solid Solution from First Principles

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 851
Author(s):  
Dong Xue ◽  
Charles W. Myles
Keyword(s):  
Thermal Expansion ◽  
Local Density ◽  
Harmonic Approximation ◽  
Negative Thermal Expansion ◽  
Entropy Change ◽  
Experimental Result ◽  
Vibrational Entropy ◽  
Electronic Density ◽  
Lower Conduction Band ◽  
X 32

We present the electronic and vibrational studies on Si136-xGex (x = 8, 32, 40, 104) alloys, using the local density approximation (LDA) scheme. We find that a “nearly-direct” band gap exists in the band structure of Si104Ge32 and Si96Ge40, when compared with the similarly reported results obtained using a different computational code. The calculated electronic density of state (EDOS) profiles for the valence band remain nearly identical and independent of the Ge concentration (x = 32, 40, 104) even though some variation is found in the lower conduction band (tail part) as composition x is tuned from 8 (or 40) to 104. The negative thermal expansion (NTE) phenomenon is explored using quasi-harmonic approximation (QHA), which takes the volume dependence of the vibrational mode frequencies into consideration, while neglecting the temperature effect on phonon anharmonicity. Determined macroscopic Grüneisen parameter trends show negative values in the low temperature regime (1 K < T < 115 K), indicating the NTE behavior found in Si128Ge8 is analogous to the experimental result for Si136. Meanwhile, calculations for the ratio of the vibrational entropy change to the volume change at several characteristic temperatures reconfirm the existence of NTE in Si128Ge8 and Si104Ge32.

scholarly journals Thermal Expansion of MgTiO3 Made by Sol-Gel Technique at Temperature Range 25–890 °C

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 887 ◽  
Author(s):  
Tamir Tuval ◽  
Brian A. Rosen ◽  
Jacob Zabicky ◽  
Giora Kimmel ◽  
Helena Dilman ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Sol Gel ◽  
Lattice Parameters ◽  
Published Data ◽  
Temperature Structure ◽  
Solid State Method ◽  
Synthesis Technique ◽  
Thermal Expansion Coefficients ◽  
Reported Data

MgTiO3 is a material commonly used in the industry as capacitors and resistors. The high-temperature structure of MgTiO3 has been reported only for materials synthesized by the solid-state method. This study deals with MgTiO3 formed at low temperatures by the sol-gel synthesis technique. Co-precipitated xerogel precursors of nanocrystalline magnesium titanates, with Mg:Ti ratio near 1:1, were subjected to thermal treatment at 1200 °C for 5 h in air. A sample with fine powders of MgTiO3 (geikielite) as a major phase with Mg2TiO4 (qandilite) as a minor phase was obtained. The powder was scanned on a hot-stage X-ray powder diffractometer at temperatures between 25 and 890 °C. The lattice parameters and the atomic positions of the two phases were determined as a function of temperature. The thermal expansion coefficients of the geikielite were derived and compared with previously published data using the solid-state synthesis technique, providing insights on trends in materials properties at elevated temperature as a function of synthesis. It was found that the deviation of the present results in comparison to previously reported data do not originate from the method of synthesis but rather from the fact that there is an asymmetric solubility gap in geikielite. The lattice parameters of this study present the property of stoichiometric MgTiO3 and are compared to previously reported non-stoichiometric MgTiO3 with excess of Ti. The values of lattice parameters of the non-stoichiometric versus temperature of geikielite found the same for both solid-state reaction and sol-gel products.

Thermal expansion of inert gas solids in the harmonic approximation

1964 ◽  
Vol 10 (1) ◽  
pp. 69-70 ◽  
Author(s):  
J.W. Leech ◽  
C.J. Peachey ◽  
J.A. Reissland
Keyword(s):  
Thermal Expansion ◽  
Harmonic Approximation ◽  
Inert Gas

Anisotropic lattice expansion of three-dimensional colloidal crystals and its impact on hypersonic phonon band gaps

2014 ◽  
Vol 16 (19) ◽  
pp. 8921 ◽  
Author(s):  
Songtao Wu ◽  
Gaohua Zhu ◽  
Jin S. Zhang ◽  
Debasish Banerjee ◽  
Jay D. Bass ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Colloidal Crystals ◽  
Band Gaps ◽  
Lattice Expansion ◽  
Phonon Band ◽  
Anisotropic Lattice

Negative Thermal Expansion of Yb2Mo3O12 and Lu2Mo3O12

2008 ◽  
Vol 368-372 ◽  
pp. 1662-1664 ◽  
Author(s):  
X.L. Xiao ◽  
M.M. Wu ◽  
J. Peng ◽  
Y.Z. Cheng ◽  
Zhong Bo Hu
Keyword(s):  
Thermal Expansion ◽  
Solid State ◽  
Solid State Reaction ◽  
Linear Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Orthorhombic Structure ◽  
Conventional Solid State Reaction ◽  
Temperature Range ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Compounds Yb2Mo3O12 and Lu2Mo3O12 were prepared by conventional solid-state reaction. Their crystal structures and thermal expansion properties were investigated. It was found that Yb2Mo3O12 and Lu2Mo3O12 adopt orthorhombic structure and show negative thermal expansion (NTE) in the temperature range of 200-800 °C. Their a-axis and c-axis exhibit stronger contraction in the temperature range of 200-800 °C, while b-axis slightly expands in the temperature range of 200-300 °C and then contracts in the temperature range of 300-800 °C. The linear thermal expansion coefficients al of Yb2Mo3O12 and Lu2Mo3O12 are −5.17 × 10−6 °C−1 and −5.67 × 10−6 °C−1, respectively.

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