Effect of point defects on the thermal transport properties of (LaxGd1- x)2Zr2O7 : Experiment and theoretical model

The equilibrium temperature (T0) at which the tetragonal and monoclinic phases of either ZrO2 or HfO2 coexist is generally defined by the middle temperature of As (the onset transformation temperature on heating) and Ms (the onset transformation temperature on cooling). It cannot be directly determined due to the athermal nature of the martensitic transformation. Practically, the determination of T0 is important for the prediction of As and Ms in ZrO2 or HfO2-based materials. In this work, the ZrO2–HfO2 system was studied experimentally by differential thermal analysis (DTA) to obtain the martensitic tetragonal ⇔ monoclinic transformation temperatures in the temperature range of 1273–1973 K. The T0 temperatures obtained for ZrO2 and HfO2 are 1367±5 and 2052±5 K, respectively. They are adopted for the assessments of the Gibbs energy parameters of these two oxides. A reasonably calculated ZrO2−HfO2 phase diagram is presented.

https://ceramics.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1551-2916.2007.01719.x

“The Zirconia−Hafnia System: DTA Measurements and Thermodynamic Calculations”

We use a combination of density functional theory and calorimetric measurements to investigate the monoclinic to tetragonal transition in hafnia and zirconia. We measure the transition enthalpies to be $8.4\ifmmode\pm\else\textpm\fi{}0.7\text{ }\text{kJ}/\text{mol}$ in hafnia and, as previously reported, $5.272\ifmmode\pm\else\textpm\fi{}0.544\text{ }\text{kJ}/\text{mol}$ in zirconia. Calculated values are 10.21 and 7.50 kJ/mol for hafnia and zirconia, respectively. We formulate a theoretical model of the phase transition consistent with the martnesitic character of the transformations. The transition barriers of 20.3 and 16.3 kJ/mol are estimated for hafnia and zirconia, respectively. We report the phonon spectra of monoclinic and tetragonal phases of both oxides and identify the Raman and IR active modes. The theoretical results compare well with available experiments. We present a comprehensive theoretical comparison of thermodynamic properties of zirconia and hafnia including the temperature dependence of specific heat.

Monoclinic to tetragonal transformations in hafnia and zirconia: A combined calorimetric and density functional study

One of the most accurate approaches for calculating lattice thermal conductivity, $$\kappa _\ell$$
 DMPSID=1
 , is solving the Boltzmann transport equation starting from third-order anharmonic force constants. In addition to the underlying approximations of ab-initio parameterization, two main challenges are associated with this path: high computational costs and lack of automation in the frameworks using this methodology, which affect the discovery rate of novel materials with ad-hoc properties. Here, the Automatic Anharmonic Phonon Library (AAPL) is presented. It efficiently computes interatomic force constants by making effective use of crystal symmetry analysis, it solves the Boltzmann transport equation to obtain $$\kappa _\ell$$
 DMPSID=2
 , and allows a fully integrated operation with minimum user intervention, a rational addition to the current high-throughput accelerated materials development framework AFLOW. An “experiment vs. theory” study of the approach is shown, comparing accuracy and speed with respect to other available packages, and for materials characterized by strong electron localization and correlation. Combining AAPL with the pseudo-hybrid functional ACBN0 is possible to improve accuracy without increasing computational requirements. A new theoretical framework could provide a more efficient method for calculating a material’s thermal conductivity. Understanding how materials conduct heat is crucial for a range of applications, from heat sinks to thermal insulation. Despite its fundamental importance, predicting a material’s lattice thermal conductivity is challenging, and often requires experimental data or knowledge of specific properties to be entered during the process. An international team of researchers led by Stefano Curtarolo from Duke University now present a framework that can predict the lattice thermal conductivity of single-crystal and polycrystalline materials using just a single input file, with no further intervention. Called the Automatic Anharmonic Phonon Library, the methods computes certain parameters using symmetry analysis, before solving the Boltzmann transport equation, providing information on both the electronic structure and phonon-dependent properties.

https://digital.library.unt.edu/ark:/67531/metadc1115853/m2/1/high_res_d/s41524-017-0046-7.pdf

An efficient and accurate framework for calculating lattice thermal conductivity of solids: AFLOW—AAPL Automatic Anharmonic Phonon Library

The previous thermodynamic modeling efforts on the Zr–O system are reviewed and examined in this work. The existing problems are summarized and a new assessment is carried out. The comparison of results of calculations by using the parameters of different versions is presented. It is demonstrated that further experimental investigations are indispensable to get a better thermodynamic assessment.

Hélène Lartigue

Papers

Specific heat capacity and Debye temperature of zirconia and its solid solution