Electrical Resistivity and Diffusionless Phase Transformations of Zirconia at High Temperatures and Ultrahigh Pressures

Abstract

The resistivity of chemically pure monoclinic zirconia has been investigated at pressures to 45,000 bars and temperatures to 1200°C. Measurements were made on thin, prepressed wafers of ZrO2 situated between the opposed, cemented carbide Bridgman anvils of a uniaxial Griggs and Kennedy simple squeezer. Observation of discontinuous changes in electrical resistance at various temperatures under isobaric conditions have been used to define the phase diagram. The pressure dependence of the temperature of the reversible monoclinic ⇌ tetragonal phase transition in zirconium dioxide agreed with the slope of the P‐T equilibrium curve up to 15 kilobars as calculated from thermodynamics, i.e., normaldT/normaldP=−3.02×10−2 degrees bar−1 false(1false( . Activation energy for electrical conduction followed the Arrhenius equation and was found to be pressure dependent, decreasing from 3.56 ev at atmospheric pressure to an apparently constant value of 0.86 ev from 30 to 45 kilobars.

Improving wear resistance of plasma-sprayed calcia and magnesia-stabilized zirconia mixed coating: roles of phase stability and microstructure

“…On cooling, the low stabilizer tetragonal phase may transform to a monoclinic structure, which has a lower free energy at lower temperatures 39 . It has been thought that the stabilization of the tetragonal phase arises from a combination of the surface energy effect and the constraint of the rigid matrix that opposes the transformation to a less dense monoclinic form 42 . In a previous study, as-sprayed ZrO 2 –24MgO top coat showed a complete non-transformable tetragonal phase up to 750 °C, however, after thermal exposure at 1000 °C for 60 h, the transformation of the tetragonal phase to the monoclinic phase was observed in the XRD patterns 33 .…”

A pressure-temperature phase diagram for zircon at extreme conditions

“…The stability of zirconia polymorphs of zirconia, including monoclinic (baddeleyite), tetragonal, cubic, and two orthorhombic polymorphs, as well as liquid zirconia, are taken from Kaiser et al (2008) and Bouvier et al (2000) and references therein (e.g., Whitney, 1965;Block et al, 1985;Ohtaka et al, 1991;Ohtaka et al, 1994;Haines et al, 1995;Haines et al, 1997). Experimental dissociation of reidite has been documented by diamond anvil cell (Liu, 1979;Tange and Takahashi, 2004) and in shocked charges (Mashimo et al, 1983).…”

Size Effects on the Stabilization of Ultrafine Zirconia Nanoparticles

“…These values are in close agreement with calculations from the contribution of the surface energy proposed by Garvie, which is considered to influence the stability of TZ particles. The pressure dependence of T c was described by Whitney in 1965 and completed more recently by the Raman technique . The size dependence of T c is described as monotonic, and Molodetsky et al even suggested the presence of cubic zirconia particles in powder obtained by calcination of amorphous zirconia.…”