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

Autor: Philipp Keuter, Anna L. Ravensburg, Marcus Hans, Soheil Karimi Aghda, Damian M. Holzapfel, Daniel Primetzhofer, Jochen M. Schneider
Jazyk: angličtina
Rok vydání: 2020
Předmět:
Zdroj: Materials, Vol 13, Iss 21, p 5021 (2020)
Druh dokumentu: article
ISSN: 1996-1944
DOI: 10.3390/ma13215021
Popis: 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.
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