Shear-driven instability in zirconium at high pressure and temperature and its relationship to phase-boundary behaviors

Abstract

Evidence in support of a shear driven anomaly in zirconium at elevated temperatures and pressures has been determined through the combined use of ultrasonic, diffractive, and radiographic techniques. Implications that these have on the phase diagram are explored through thermoacoustic parameters associated with the elasticity and thermal characteristics. In particular, our results illustrate a deviating phase boundary between the α and ω phases, referred to as a kink, at elevated temperatures and pressures. Further, pair distribution studies of this material at more extreme temperatures and pressures illustrate the scale on which diffusion takes place in this material. Possible interpretation of these can be made through inspection of shear-driven anomalies in other systems.

Melting curve of elemental zirconium

“…The high melting point (2128 K) of Zr often classifies it as a refractory metal. Although there are some works in the high temperature behavior of zirconium at high pressures [8][9][10][11] , its melting curve has not yet been investigated and this absence of experimental data has strongly motivated this study. On the other hand, the high pressure melting of transition metals has always been a subject of intense debate, because of the large uncertainties in the temperature measurements and the criteria used to identify the melting, so that different approaches can yield very different results.…”

Elasticity of nanocrystalline kyanite at high pressure and temperature from ultrasonic and synchrotron X‐ray techniques

“…Elastic constants are one of the elementary characteristics of materials and essential for the modeling of mechanical properties 1,2 (eg, plastic deformation or fracture), and microstructure simulations during phase transformations and materials processing 3 as well as the calculation of mechanical properties, 4 such as the hardness. Although materials’ elasticity can be readily investigated at ambient conditions using, for example, ultrasonic techniques, their measurement at extreme conditions of pressure and temperature becomes highly challenging 5 . However, measurements of elastic moduli as a function of temperature and pressure have increasingly attracted attention not only for discovering novel superhard materials 6–9 but also for engineering purposes.…”

“…Nonetheless, a full set of elasticity requires both the bulk and shear moduli, and their derivations of pressure and temperature. Despite remaining a challenging task, these data and further parameters 5 (eg, elastic Debye temperature, acoustic Grüneisen parameter, or thermal conductivity) can be observed by integrating ultrasonic measurements with in situ synchrotron X‐ray studies at high P ‐ T that has successfully been probed in mineral physics 19,20 . However, these techniques have only been transferred to the field of material sciences to a limited extent, for example, to study phase relations in metals 5,21 …”

“…A well‐known technique for exploring the bulk modulus of materials and its pressure evolution is in situ synchrotron X‐ray diffraction under high pressure 5 . This process is followed by applying equation of states (EoS) to the acquired pressure‐volume ( P ‐ V ) data, for example, the Birch‐Murnaghan EoS 18 written in its third order asEquation () relates the unit‐cell volume V P ,300 at room temperature to the pressure P with the parameters K T 0 for the isothermal bulk modulus, for the first pressure derivation of the isothermal bulk modulus, and V 0 ,300 as the unit‐cell volume at atmospheric pressure and temperature.…”

“…19,20 However, these techniques have only been transferred to the field of material sciences to a limited extent, for example, to study phase relations in metals. 5,21 Within this study, we have applied the in situ synchrotron and imaging X-ray techniques combined with the ultrasonic measurement at high P-T on transparent nano-polycrystalline ceramics (nanoceramics). This new type of materials with tantalizing mechanical properties compared to the corresponding single crystals can be synthesized at extreme pressure and temperature conditions and becomes increasing attention for photonic applications, such as for mechanically resistant optical windows.…”