scholarly journals Lattice thermal expansion of complex oxides with intrinsic anharmonicity

2014 ◽  
Vol 70 (a1) ◽  
pp. C161-C161
Author(s):  
M. Mangir Murshed ◽  
Pei Zhao ◽  
Evgeny Alekseev ◽  
Ashfia Huq ◽  
Thorsten Gesing
Keyword(s):  
Thermal Expansion ◽  
Frequency Distribution ◽  
Cutoff Frequency ◽  
Negative Thermal Expansion ◽  
Complex Oxides ◽  
Debye Model ◽  
Quality Data ◽  
Lattice Thermal Expansion ◽  
Before And After ◽  
Intrinsic Anharmonicity

The lattice thermal expansion of crystalline solids cannot be adequately modeled by Grüneisen approximation using either Einstein single harmonic frequency or Debye frequency spectrum because a true phonon spectrum does not follow either of the two kinds. The Debye model misfits to many observations due to the fact that real solids comprises of axial anisotropy, lattice waves with dispersion at the Brillouin zone boundaries, low/high frequency optical vibrations in excess of the Debye spectrum. The actual frequency distribution is a complicated function of frequency instead of a simple parabolic Debye spectrum. The frequency distribution can be simplified using power series [1] leading to singularities before and after the Debye cutoff frequency. Using multiple Debye or Einstein oscillators, or their mixtures, is also common practice to better describe the lattice expansion, however, these models extremely suffer from intrinsic anharmonicity in particular at high temperatures. It was demonstrated that even the noble monoatomic solids required inclusion of anharmonic terms in the harmonic model to better explain the observed values [2]. Worse even, when anharmonicity becomes dominant due to formation of vacancies and defects, anomalies of hard/soft modes or change of stereochemical activities of lone electron pairs (LEPs) as function of temperature. Herein we approach an extended Grüneisen approximation that includes harmonic, quasiharmonic and intrinsic anharmonic potentials to describe the internal energy of the crystal as function of temperature. The model has been applied to several complex oxides with LEPs (Bi2Ga4O9[3]) along with axial negative thermal expansion (PbFeBO4) and rigid-unit-modes (KAsW2O9) reported here. The metric parameters were obtained from quality data collected from temperature-dependent neutron and X-ray powder diffractions.

Raman Band Redshifting of α-Cu2(OH)3Cl with Decreasing the Temperature

2012 ◽  
Vol 430-432 ◽  
pp. 391-394
Author(s):  
Xiao Dong Liu ◽  
Xing Liang Xu ◽  
Dong Dong Meng ◽  
Masayoshi Fujihala ◽  
Xu Guang Zheng ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Laser Heating ◽  
Raman Band ◽  
Negative Thermal Expansion ◽  
Polycrystalline Sample ◽  
Heating Effect ◽  
Lattice Thermal Expansion ◽  
Geometric Frustration ◽  
Thermal Expansion Effect ◽  
Expansion Effect

Raman spectra of the magnetic geometric frustration material – the botallackite-structure α-Cu2(OH)3Cl polycrystalline sample were measured down to liquid N2 temperature. It is found that the hydroxyl stretching bands shift abnormally according to the lattice thermal expansion effect of normal materials, i.e., they redshift with decreasing the sample temperature (negative thermal expansion) using liquid N2 cooling while other bands blueshift. This abnormality was also confirmed by observing the band-shifting caused by local laser heating effect using different laser powers, and can be qualitatively explained by checking the local hydroxyl environment with a trimeric hydrogen bond.

scholarly journals Low-Temperature Spark Plasma Sintering of ZrW2−xMoxO8 Exhibiting Controllable Negative Thermal Expansion

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1582 ◽  
Author(s):  
Hui Wei ◽  
Marin Hasegawa ◽  
Shunsuke Mizutani ◽  
Akihisa Aimi ◽  
Kenjiro Fujimoto ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Spark Plasma Sintering ◽  
Structure Refinement ◽  
Negative Thermal Expansion ◽  
Thermomechanical Analysis ◽  
Disorder Phase Transition ◽  
Plasma Sintering ◽  
Before And After ◽  
Spark Plasma

Molybdenum-doped zirconium tungstate (ZrW2−xMoxO8) has been widely studied because of its large isotropic coefficient of negative thermal expansion (NTE). However, low density and poor sinterability limit its production and application. In this study, relative density greater than 90% single-phase ZrW2−xMoxO8 (0.0 ≤ x ≤ 1.0) sintered bodies were fabricated by spark plasma sintering (500–600 °C for 10 min) using ZrW2−xMoxO7(OH)2·2H2O precursor powders as the starting material. High-temperature X-ray diffraction and thermomechanical analysis were used to investigate the change in the order–disorder phase transition temperature of the sintered materials; it gradually dropped from 170 °C at x = 0.0 to 78 °C at x = 0.5, and then to below room temperature at x ≥ 0.7. In addition, all sintered bodies exhibited NTE behavior. The NTE coefficient was controllable by changing the x value as follows: from −7.85 × 10−6 °C−1 (x = 0) to −9.01 × 10−6 °C−1 (x = 0.6) and from −3.22 × 10−6 °C−1 (x = 0) to −2.50 × 10−6 °C−1 (x = 1.0) before and after the phase transition, respectively. Rietveld structure refinement results indicate that the change in the NTE coefficient can be straightforwardly traced to the thermodynamic instability of the terminal oxygen atoms, which only have one coordination.

Effect of preset interfacial ZrB2 particles on the microstructure and properties of C/C-AlSi composites

2021 ◽  
pp. 002199832110046
Author(s):  
Wei Feng ◽  
Chengwei Tang ◽  
Lei Liu ◽  
Jian Chen ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Thermal Expansion ◽  
Thermal Shock ◽  
Retention Rate ◽  
Pressure Infiltration ◽  
Micro Scale ◽  
Before And After ◽  
Micro Morphology ◽  
Strength Retention ◽  
Fiber Fabric

ZrB2 particles were preset to the C-AlSi interface to improve oxidation resistance of C/C preform and adjust the microstructure of the interpenetrated C/C-AlSi composite prepared through pressure infiltration of eutectic AlSi into a fiber fabric based porous C/C skeleton. Micro-morphology investigations suggested that the AlSi textures were changed from dendritic to petals-like state, and the nano to micro-scale ZrB2 particles were dispersed into AlSi and affected the distribution of Al and Si nearby carbon. Tests demonstrated that C/C-AlSi have slight lower density and thermal expansion coefficient, and higher original compressive strength, while C/C-ZrB2-AlSi composites presented an outstanding strength retention rate after thermal shock. Fracture and micro-morphology indicated that the influence of the preset ZrB2 to the interface of carbon and alloy greatly affected the generation and propagation of cracks, which determined the diverse compression behaviors of the composites before and after thermal shock.

Polarization- and Strain-Mediated Control of Negative Thermal Expansion and Ferroelasticity in BiInO3–BiZn1/2Ti1/2O3

2021 ◽  
Vol 33 (4) ◽  
pp. 1498-1505
Author(s):  
Takumi Nishikubo ◽  
Takahiro Ogata ◽  
Lalitha Kodumudi Venkataraman ◽  
Daniel Isaia ◽  
Zhao Pan ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Negative Thermal Expansion

scholarly journals Negative thermal expansion in YbMn2Ge2 induced by the dual effect of magnetism and valence transition

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Yongqiang Qiao ◽  
Yuzhu Song ◽  
Andrea Sanson ◽  
Longlong Fan ◽  
Qiang Sun ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Intermetallic Compound ◽  
Cell Volume ◽  
Valence State ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Combined Effect ◽  
Dual Effect ◽  
Valence Transition ◽  
Magnetovolume Effect

AbstractNegative thermal expansion (NTE) is an intriguing property, which is generally triggered by a single NTE mechanism. In this work, an enhanced NTE (αv = −32.9 × 10−6 K−1, ΔT = 175 K) is achieved in YbMn2Ge2 intermetallic compound to be caused by a dual effect of magnetism and valence transition. In YbMn2Ge2, the Mn sublattice that forms the antiferromagnetic structure induces the magnetovolume effect, which contributes to the NTE below the Néel temperature (525 K). Concomitantly, the valence state of Yb increases from 2.40 to 2.82 in the temperature range of 300–700 K, which simultaneously causes the contraction of the unit cell volume due to smaller volume of Yb3+ than that of Yb2+. As a result, such combined effect gives rise to an enhanced NTE. The present study not only sheds light on the peculiar NTE mechanism of YbMn2Ge2, but also indicates the dual effect as a possible promising method to produce enhanced NTE materials.

Nanoparticle Superlattices with Negative Thermal Expansion (NTE) Coefficients

2021 ◽  
Author(s):  
Hyeong Jin Kim ◽  
Wenjie Wang ◽  
Surya Mallapragada ◽  
Alex Travesset ◽  
David Vaknin
Keyword(s):  
Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Nanoparticle Superlattices
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