Low thermal conductivity of the negative thermal expansion material, HfMo2O8

2007 ◽  
Vol 90 (15) ◽  
pp. 151906 ◽  
Author(s):  
Catherine A. Kennedy ◽  
Mary Anne White ◽  
Angus P. Wilkinson ◽  
Tamas Varga
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Low Thermal Conductivity

Reduced Thermal Conductivity by Low-Frequency Optic Phonons that Give Rise to Negative Thermal Expansion: Opportunities for Thermoelectrics?

2007 ◽  
Vol 1044 ◽  
Author(s):  
Mary Anne White ◽  
Catherine A. Whitman
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Electronic Properties ◽  
Thermoelectric Materials ◽  
Negative Thermal Expansion ◽  
Low Frequency ◽  
Acoustic Phonons ◽  
Low Thermal Conductivity ◽  
Efficient Coupling

AbstractWe have recently found that the negative thermal expansion (NTE) materials, ZrW2O8 and HfMo2O8, show exceptionally low thermal conductivity. We surmise that the mechanism is the efficient coupling of the low-frequency optic phonons that give rise to negative thermal expansion with the heat-carrying acoustic phonons. Although neither ZrW2O8 nor HfMo2O8 has suitable electronic properties for thermoelectric applications, perhaps the principle of reduced thermal conductivity by low-frequency optic phonons in NTE materials can be used to develop more efficient thermoelectric materials.

Primary pyroelectric transition temperatures of binary nitrides (AlN, GaN and InN)

2019 ◽  
Vol 33 (05) ◽  
pp. 1950049
Author(s):  
Muralidhar Swain ◽  
Sushant K. Sahoo ◽  
Bijay K. Sahoo
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Negative Thermal Expansion ◽  
Polarization Field ◽  
Piezoelectric Polarization ◽  
Polarization Mechanism ◽  
Prior Literature

The primary pyroelectric transition temperature of wurtzite nitrides (AlN, GaN and InN) has been explored theoretically from their thermal properties. The spontaneous and piezoelectric polarization modifies the thermal conductivity of nitrides. The thermal conductivity [Formula: see text] as a function of temperature including and excluding the polarization mechanism predicts a transition temperature [Formula: see text] between primary and secondary pyroelectric effects. Below [Formula: see text], thermal conductivity including polarization field [Formula: see text] is lesser than thermal conductivity excluding polarization field [Formula: see text]. This is due to negative thermal expansion in binary nitrides below [Formula: see text]; however, above [Formula: see text], [Formula: see text]. [Formula: see text] is significantly contributed by piezoelectric polarization above [Formula: see text] due to thermal expansion which is the reason for the secondary pyroelectric effect. The transition temperature [Formula: see text] for AlN, GaN and InN has been predicted as 100 K, 70 K and 60 K, respectively, which fit well with the prior literature studies. This report proposes that thermal properties’ study can reveal the role of acoustic phonons in pyroelectricity.

scholarly journals High-entropy (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 with good high temperature stability, low thermal conductivity and anisotropic thermal expansivity

2020 ◽  
Author(s):  
Zifan Zhao ◽  
Huimin Xiang ◽  
Heng Chen ◽  
Fu-zhi Dai ◽  
Xiaohui Wang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Rare Earth ◽  
High Temperature ◽  
Phase Stability ◽  
Temperature Phase ◽  
Low Thermal Conductivity ◽  
High Entropy ◽  
Anisotropic Thermal Expansion

Abstract The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) including good tolerance to harsh environments, thermal expansion match with the interlayer mullite, good high-temperature phase stability and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high entropy ceramics. The as-synthesized (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits close thermal expansion coefficient (6.96×10-6 /K at 300-1473 K) to that of mullite, good phase stability from 300 K to 1473 K, and low thermal conductivity (1.50 W·m-1·K-1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms while the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare earth cations.

Ultralow thermal conductivity and negative thermal expansion of CuSCN

Nano Energy ◽  
2020 ◽  
Vol 73 ◽  
pp. 104822 ◽  
Author(s):  
Yupeng Shen ◽  
Fancy Qian Wang ◽  
Qian Wang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Negative Thermal Expansion

ANOMALOUS LATTICE PROPERTIES OF ZrNiSn CAUSED BY ELECTRON LOCALIZATION

1993 ◽  
Vol 07 (01n03) ◽  
pp. 383-386 ◽  
Author(s):  
F. G. ALIEV ◽  
V. V. PRYADUN ◽  
R. VILLAR ◽  
S. VIEIRA ◽  
J. M. CALLEJA ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Seebeck Coefficient ◽  
Raman Spectra ◽  
Negative Thermal Expansion ◽  
Electron Interaction ◽  
Electron Localization ◽  
Conduction Electrons ◽  
Isostructural Phase Transition

Thermal transport (resistivity, Seebeck coefficient, thermal conductivity), thermal expansion and Raman spectra of the intermetallic ordered vacancy compound ZrNiSn was studied. Below T = 100 K an isostructural phase transition was observed. Analyzing ZrNiSn properties, we conclude that this transition is related to freezing of Ni atoms in some of equivalent positions. Conduction electrons, delocalized by increasing order at T < 100 K , show a new localization below 20K. In this range, an anomalous negative thermal expansion, possibly caused by electron-electron interaction was seen.

scholarly journals High-entropy (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 with good high temperature stability, low thermal conductivity and anisotropic thermal expansivity

2020 ◽  
Author(s):  
Zifan Zhao ◽  
Huimin Xiang ◽  
Heng Chen ◽  
Fu-zhi Dai ◽  
Xiaohui Wang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Rare Earth ◽  
High Temperature ◽  
Phase Stability ◽  
Temperature Phase ◽  
Low Thermal Conductivity ◽  
High Entropy ◽  
Anisotropic Thermal Expansion

Abstract The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) including good tolerance to harsh environments, thermal expansion match with the interlayer mullite, good high-temperature phase stability and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high entropy ceramics. The as-synthesized (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits close thermal expansion coefficient (6.96×10-6 /K at 300-1473 K) to that of mullite, good phase stability from 300 K to 1473 K, and low thermal conductivity (1.50 W·m-1·K-1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms while the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare earth cations.

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