Efficient first-principles evaluation of thermodynamic stability, physical properties and photocatalytic performance of alkali-metal tantalates

We report the structure, stability, electronic, optical, and photocatalytic properties of sodium and potassium tantalates (NaTaO3 and KTaO3) by employing meta-GGA level DFT calculations. Our results show that the structural, mechanical, vibrational, and energetic properties computed using SCAN meta-GGA are in excellent agreement with experimental data compared to earlier calculations performed using semi-local and hybrid-DFT calculations. Moreover, we also show that the employment of TB09 meta-GGA with spin-orbit coupling facilitates reliable description of the electronic properties of NaTaO3 and KTaO3. The optical absorption coefficients of orthorhombic NaTaO3 and cubic KTaO3 are also reported and their potential for photocatalytic hydrogen production from overall water molecule splitting has been examined. Our results clearly show that accurate determination of physical properties of NaTaO3 and KTaO3 can be achieved by combining SCAN and TB09 meta-GGAs at a significantly lower computational cost compared to computationally demanding hybrid-DFT and GW calculations.</p

Evaluation of thermodynamics, formation energetics and electronic properties of vacancy defects in CaZrO3

Using first-principles total energy calculations we have evaluated the thermodynamics and the electronic properties of intrinsic vacancy defects in orthorhombic CaZrO3. Charge density calculations and the atoms-in-molecules concept are used to elucidate the changes in electronic properties of CaZrO3 upon the introduction of vacancy defects. We explore the chemical stability and defect formation energies of charge-neutral as well as of charged intrinsic vacancies under various synthesis conditions and also present full and partial Schottky reaction energies. The calculated electronic properties indicate that hole-doped state can be achieved in charge neutral Ca vacancy containing CaZrO3 under oxidation condition, while reduction condition allows to control the electrical conductivity of CaZrO3 depending on the charge state and concentration of oxygen vacancies. The clustering of neutral oxygen vacancies in CaZrO3 is examined as well. This provides useful information for tailoring the electronic properties of this material. We show that intentional incorporation of various forms of intrinsic vacancy defects in CaZrO3 allows to considerably modify its electronic properties, making this material suitable for a wide range of applications

Improved thermodynamic stability and visible light absorption in Zr+X codoped (X = S, Se and Te) BaTiO₃ photocatalysts:A first-principles study

Band gap tuning of titanium based perovskite oxides through chalcogen doping is an attractive avenue for realizing visible light driven photocatalysis for hydrogen production. Unfortunately, accommodating a chalcogen atom at an O-site of BaTiO3 is thermodynamically challenging owing to large differences in the atomic radii and electronegativities of oxygen and chalcogen atoms. In the present study we employ first-principles density functional theory calculations to examine the influence of Zr codoping on the structural, thermodynamic, opto-electronic properties and photocatalytic performance of X-doped (X = S, Se and Te) BaTiO3 systems. The atomic structure and energetic properties are computed using SCAN meta-GGA functional of density functional theory, while the electronic and optical properties are computed using the TB-mBJ meta-GGA potential functional. Within the valid limits of the atomic chemical potentials, we find that chalcogen doping in BaTiO3 lattice would be experimentally difficult despite a clear reduction in the electronic band gap of this system useful for application in visible light driven photocatalysis. In order to improve the synthesis feasibility of X-doped BaTiO3 under oxygen-rich as well as oxygen-poor chemical environments, we propose Zr as a codopant at a Ti-site in X-doped BaTiO3 which improves the thermodynamic stability and also retains the reduction in the electronic band gap of BaTiO3 caused by the presence of chalcogen atom. Our results suggest that Zr+X (X = S, Se and Te) codoped BaTiO3 offers great opportunities as a practical photocatalysts for hydrogen production through overall splitting of the water molecule.</p

Formation energies and electronic structure of intrinsic vacancy defects and oxygen vacancy clustering in BaZrO₃

Thermodynamically stable oxygen vacancy clustering in the ZrO2 layer of BaZrO3 gives rise to n-type behaviour which originates from the charge delocalization of the in-plane unbound Zr1-4d electrons.</p