scholarly journals A Proposal for a Composite with Temperature-Independent Thermophysical Properties: HfV2–HfV2O7

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5021
Author(s):  
Philipp Keuter ◽  
Anna L. Ravensburg ◽  
Marcus Hans ◽  
Soheil Karimi Aghda ◽  
Damian M. Holzapfel ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Temperature Coefficient ◽  
Thermophysical Properties ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Phase Fraction ◽  
Formation Temperature ◽  
Oxygen Mobility ◽  
Zero Temperature ◽  
Coefficient Of Elasticity

The HfV2–HfV2O7 composite is proposed as a material with potentially temperature-independent thermophysical properties due to the combination of anomalously increasing thermoelastic constants of HfV2 with the negative thermal expansion of HfV2O7. Based on literature data, the coexistence of both a near-zero temperature coefficient of elasticity and a coefficient of thermal expansion is suggested for a composite with a phase fraction of approximately 30 vol.% HfV2 and 70 vol.% HfV2O7. To produce HfV2–HfV2O7 composites, two synthesis pathways were investigated: (1) annealing of sputtered HfV2 films in air to form HfV2O7 oxide on the surface and (2) sputtering of HfV2O7/HfV2 bilayers. The high oxygen mobility in HfV2 is suggested to inhibit the formation of crystalline HfV2–HfV2O7 composites by annealing HfV2 in air due to oxygen-incorporation-induced amorphization of HfV2. Reducing the formation temperature of crystalline HfV2O7 from 550 °C, as obtained upon annealing, to 300 °C using reactive sputtering enables the synthesis of crystalline bilayered HfV2–HfV2O7.

Growth, structural and thermophysical properties of TbNbO4 crystals

CrystEngComm ◽  
2018 ◽  
Vol 20 (10) ◽  
pp. 1455-1462 ◽  
Author(s):  
Jiayi Guo ◽  
Junyu Ren ◽  
Rui Cheng ◽  
Qing Dong ◽  
Cunyuan Gao ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Thermophysical Properties ◽  
Negative Thermal Expansion

An as-grown TbNbO4 crystal has a negative thermal expansion and the zero thermal expansion could be achieved.

High Temperature Stability of Zirconium Tungstate

2020 ◽  
Vol 993 ◽  
pp. 771-775
Author(s):  
Ping Zhai ◽  
Xiao Feng Duan ◽  
Da Qian Chen
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Solid Phase ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Tungstic Acid ◽  
High Temperature Stability ◽  
Zirconium Tungstate

In this paper, zirconium tungstate ceramic with negative thermal expansion coefficients was prepared from zirconium oxide and tungstic acid by solid phase synthesis and high temperature quenching technique with a sintering temperature of 1200 °C. The phase structure of the material was determined by X ray and the thermal expansion coefficient was measured by dilatometer, while the TG-DTA analysis of the prepared material was also carried out. The results showed that zirconium tungstate with high purity could be obtained by rapid chilled while fired at 1200 °C. The coefficient of thermal expansion at 300 °C was minus 8.5413 × 10-6K-1, which is identical with the theoretical value. The thermal expansion coefficient of the material was negative fired lower than 750 °C, while it was positive fired higher than 750 °C, and this indicates that the decomposition temperature of zirconium tungstate is about 750 °C.

scholarly journals Micro-structured medium with large isotropic negative thermal expansion

2019 ◽  
Vol 475 (2232) ◽  
pp. 20190468 ◽  
Author(s):  
Luigi Cabras ◽  
Michele Brun ◽  
Diego Misseroni
Keyword(s):  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Simple Relation ◽  
Space Structures ◽  
New Class ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Innovative Materials ◽  
New Generation

A challenge in nano- and micro-mechanics is the realization of innovative materials exploiting auxetic behaviour to tailor thermal expansion properties. For this purpose, a new class of micro-structured media possessing an extremely wide range of tunable (positive, negative or even zero) thermal expansion is proposed and analytically and experimentally assessed. For this class of isotropic Mechanical-Auxetic Thermal-Shrinking media, the effective coefficient of thermal expansion is explicitly linked to two microstructural variables via a simple relation, allowing the design with desired values. The theoretical predictions for the negative thermal properties are fully validated by the experimental and numerical outcomes. The simplicity of the proposed structure makes the design useful for the production of a new generation of advanced media, with applications ranging from micromechanical devices to large civil and space structures.

Size and crystal symmetry breaking effects on negative thermal expansion in ScF3 nanostructures

2021 ◽  
Author(s):  
Chunyan Wang ◽  
Dahu Chang ◽  
Junfei Wang ◽  
Qilong Gao ◽  
Yinuo Zhang ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Symmetry Breaking ◽  
Coefficient Of Thermal Expansion ◽  
Negative Thermal Expansion ◽  
Crystal Symmetry ◽  
Negative Coefficient ◽  
Membrane Vibration

New membrane vibration and surface symmetry breaking effects determine the negative coefficient of thermal expansion at the nanoscale.

scholarly journals Thermally stable and highly efficient red-emitting Eu3+-doped Cs3GdGe3O9 phosphors for WLEDs: non-concentration quenching and negative thermal expansion

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Peipei Dang ◽  
Guogang Li ◽  
Xiaohan Yun ◽  
Qianqian Zhang ◽  
Dongjie Liu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Expansion ◽  
White Light ◽  
Coefficient Of Thermal Expansion ◽  
Internal Quantum Efficiency ◽  
Negative Thermal Expansion ◽  
Concentration Quenching ◽  
Excellent Thermal Stability ◽  
Red Phosphor ◽  
Highly Efficient

AbstractRed phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 − xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1–1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175–250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = −5.06 × 10−5/°C, 25–250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials.

Thermophysical Properties of Molybdenum Copper Multilayer Composites for Thermal Management Applications

2015 ◽  
Vol 825-826 ◽  
pp. 297-304 ◽  
Author(s):  
Martin Seiss ◽  
Tobias Mrotzek ◽  
Norbert Dreer ◽  
Wolfram Knabl
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Management ◽  
Thermophysical Properties ◽  
Copper Content ◽  
Coefficient Of Thermal Expansion ◽  
Strong Anisotropy ◽  
Multilayer Composites ◽  
Properties Of Materials ◽  
Materials Used

The key properties of materials used for thermal management in electronics are thermal conductivity and the coefficient of thermal expansion. These properties can be tailored by stacking molybdenum and copper layers. Here, molybdenum copper multilayer composites with varying copper content, from 63 to 88 wt%, have been investigated. It is demonstrated, that thermal conductivity and coefficient of thermal expansion, can be adjusted by the copper content. Two flash methods for measuring the thermal conductivity are compared and the validity of the results is discussed since measurements on thin materials with strong anisotropy require a certain setup of the measurement device. For the studied compositions the thermal conductivity was determined to be between 220 to 270 W/m/K and the coefficient of thermal expansion between 6.1 to 11.5 ppm/K.

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