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High‐pressure structural stability, equation of state, and thermal expansion behavior of cubic HfO 2
Author(s) -
Irshad K. A.,
Srihari Velaga,
Kumar D. Sanjay,
Ananthasivan K.,
Jena Hrudananda
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17266
Subject(s) - thermal expansion , monoclinic crystal system , bulk modulus , equation of state , thermodynamics , rietveld refinement , materials science , phase (matter) , thermal stability , compressibility , crystallography , phase transition , crystal structure , chemistry , composite material , physics , organic chemistry
The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO 2 , an ultra‐high‐temperature ceramic, have been investigated using X‐ray diffraction at extreme conditions of pressures and temperatures. High‐pressure studies show that the cubic structure is stable up to 26.2 GPa, while the high‐temperature studies show the stability of the cubic structure up to 600°C. The Rietveld structure refinement of the high‐pressure data reveals the progressive transition of secondary monoclinic phase to the cubic phase at higher pressures. The phase progression is accompanied by incompressibility along the b axis and a large compressibility along the c axis of the monoclinic structure. The second‐order Birch‐Murnaghan equation of state fit to the unit cell volume data yielded a bulk modulus of 242(16) GPa for the cubic structure. A linear thermal expansion value of α a(c) = 8.80(15) × 10 −6 °C −1 and a volume thermal expansion value of α v = 26.5(4) × 10 −6 °C −1 have been determined from the in situ high‐temperature X‐ray diffraction studies. The results are discussed by comparing with the high‐pressure and high‐temperature behavior of isostructural ZrO 2 . To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO 2 at high pressures.