High‐pressure structural stability, equation of state, and thermal expansion behavior of cubic HfO₂

Abstract

The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO2, 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 αa(c) = 8.80(15) × 10−6°C−1 and a volume thermal expansion value of αv = 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 ZrO2. To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO2 at high pressures.

Structure and microwave dielectric characteristics of Hf1‐xTixO2 ceramics

“…Recently, Wang et al reported the dielectric properties of pure and Gd-doped HfO 2 ceramics. 12 On the other hand, the HfO 2 -TiO 2 system has attracted a lot of interest, [13][14][15] owing to its extremely low thermal expansion coefficient. Tilloca reported that HfO 2 -TiO 2 ceramics had been proven to have ultralow expansion and refractory properties.…”

Understanding the Pressure Effect on the Elastic, Electronic, Vibrational, and Bonding Properties of the CeScO3Perovskite

“…According to this study, CeScO 3 is highly stable under compression, which contrasts with the behavior of other perovskites. In special, structural phase transition do not take place up to 40 GPa, which is important for applications designed to work under high stresses . However, little more is known on the influence of pressure on the physical properties of CeScO 3 , in particular, the electronic, vibrational, and elastic properties.…”

Accurate First‐Principles Treatment of the High‐Temperature Cubic Phase of Hafnia

“…Evaluated at 0 GPa we find a bulk modulus of B 0 ¼ 180 GPa, which decreases to 120 GPa over the range of 2100 to 3100 K. This drastic softening is expected as we are approaching the melting point of the material. In their recent study, Irshad et al [40] measured the bulk modulus of pressure-stabilized, nanocrystalline c À HfO 2 at ambient temperature, finding B 0 ¼ 242ð16Þ GPa. Applying a small pressure of 4 GPa (corresponding to a volume change of 1.5% ) to our result, yields a comparable bulk modulus of about 210 GPa at 2100 K, decreasing to 170 GPa at 3100 K.…”