Thermal properties of the orthorhombic CaSnO3 perovskite under pressure from ab initio quasi-harmonic calculations

Abstract

Structural, elastic and thermodynamic properties of the orthorhombic CaSnO 3 perovskite are theoretically investigated at the ab initio level as a function of temperature and pressure. Harmonic and quasiharmonic lattice dynamical calculations are performed with the Crystal program, by explicitly accounting for thermal expansion effects and by exploring the effect of several DFT functionals. The anisotropic, directional elastic response of the system is characterized up to 20 GPa of pressure. The thermal lattice expansion and elastic bulk modulus are described at simultaneous temperatures up to 2000 K and pressures up to 20 GPa. The Gibbs free energy of formation of CaSnO 3 from CaO and SnO 2 as a function of temperature is also addressed by means of fully-converged phonon dispersion calculations on the three systems.

Thermodynamic and Elastic Properties of Grossular at High Pressures and High Temperatures: A First‐Principles Study

“…The thermal expansion of grossular at different pressures and temperatures is shown in Figure a, and the value at ambient conditions is listed in Table . Our results agree well with the experimental data at relatively low temperature (Isaak et al, ) but slightly deviates from experimental data when temperature is >900 K. This deviation is typical for the QHA calculations and were also observed in pervious QHA calculations for other minerals (e.g., Erba et al, ; Maul et al, ; Wu, ). The QHA calculations assume that phonon frequencies are independent on temperature and ignore the intrinsic anharmonicity effect, which is negligible at low temperature but becomes noticeable at high temperature and low pressure.…”

“…The QHA calculations assume that phonon frequencies are independent on temperature and ignore the intrinsic anharmonicity effect, which is negligible at low temperature but becomes noticeable at high temperature and low pressure. However, the anharmonicity effect is much less pronounced at high pressures (e.g., Erba et al, 2015; Maul et al, ; Wu, ). The heat capacity at constant volume and at constant pressure is shown in Figures c and d, respectively.…”

“…The calculated elastic constants at static conditions are consistent with previous LDA calculations (Kawai & Tsuchiya, ), but larger than those calculated using generalized gradient approximation (Kawai & Tsuchiya, ) and hybrid functional B3LYP (Erba, Mahmoud, Belmonte, et al, ). This is because the generalized gradient approximation and B3LYP calculations predict a much larger volume than the LDA calculations and elasticity is sensitive to the volume (e.g., Maul et al, ; Wang & Wu, ). The vibrational contribution expands volume of grossular by ~2% (Figure ) and hence decreases C 11 , C 12 , and C 44 by ~5.6%, ~6.8%, and ~3.0% (Figure ) at ambient conditions, respectively.…”

Quantum‐mechanical condensed matter simulations with CRYSTAL

“…The fully automated implementation of the QHA in the CRYSTAL program has been applied to study several thermal properties (structural, elastic, thermodynamic, electronic) of various systems with different chemical features in the last couple of years: fully covalent diamond (Erba, 2014), ionic MgO and CaO (Erba, Shahrokhi, Moradian, & Dovesi, 2015), LiF (Erba, Maul, Itou, Dovesi, & Sakurai, 2015), mixed ionic/covalent corundum α-Al 2 O 3 (Erba, Maul, Demichelis, & Dovesi, 2015), forsterite α-Mg 2 SiO 4 (Erba, Maul, De La Pierre, & Dovesi, 2015), calcium stannate CaSnO 3 (Maul, Santos, Sambrano, & Erba, 2016), and the molecular crystals of urea, purine, and carbamazepine (Brandenburg, Potticary, Sparkes, Price, & Hall, 2017;Erba, Maul, & Civalleri, 1820;Ruggiero, Zeitler, & Erba, 2017). Some considerations can be done: (a) in all cases, the evaluation of the vibration frequencies at just four volumes ensured stable and reliable results; (b) at variance with the determination of absolute values of constant-volume thermodynamic functions (which requires phonon dispersion to be carefully taken into account), the volume dependence of such thermodynamic quantities shows a fast convergence with respect FIGURE 4 Thermal expansion coefficient of MgO periclase as determined experimentally (Anderson, Isaak, & Oda, 1992;Ganesan, 1962;White & Anderson, 1966) (black symbols) and through quasi-harmonic lattice dynamical simulations (Erba, Shahrokhi, Moradian, & Dovesi, 2015) (black line).…”

CaSnO 3 obtained by modified Pechini method applied in the photocatalytic degradation of an azo dye

“…The modes at 1079 and 1092 cm -1 were assigned to calcium carbonate vibrations [36]. Maul et al [37] performed a harmonic analysis of CaSnO 3 and presented the phonon density of states (PDOS) to correlate the contribution of Ca 2+ , Sn 4+ and O 2-movements (apical and equatorial) with the dislocation frequency (ν). According to the authors, the bands between 100 and 300 cm -1 have higher contribution of Ca 2+ and Sn 4+ atoms and small contribution of apical O 2-; for frequencies higher than 300 cm -1 , the highest contribution is from oxygen ions.…”