First-principles Investigation of CaV$_2$TeO$_8$: A Multifunctional Heteroanionic Oxychalcogenide for Photocatalytic and Thermoelectric Applications (2501.05774v2)

Abstract: The development of industrial growth raises global energy demand. Novel materials with promising unorthodox features satiate and demand for sustainable, non-toxic, and cost-effective energy. A first-principles investigation were carried out to ground state and transport properties of CaV$_2$TeO$_8$ towards energy harvesting and photocatalytic applications was carried out. In groundstate the CaV$_2$TeO$_8$ showed good mechanically stable with a volume of (1138.235 \text{\AA}^3) and a high elastic modulus of (215.73 GPa). Further, the electronic properties of CaV$_2$TeO$_8$, PBE-GGA exchange-correlation was utilized, demonstrates direct and indirect transitions with a wide bandgap of 2.7 and 2.8 eV, indicating its semiconducting nature. Photoinduced charge carriers were investigated through Deformation Potential Theory (DPT) to estimate the mobility of charge carriers, excitonic radius, and effective mass. Axial anisotropic strain in band degeneracy and shifts in the S-Y and Y-\Gamma transitions offer a (3.17 \text{\AA}^3) Frenkel-type strongly bound exciton with a high carrier mobility of (2409.91 \, \text{cm}^2 \, \text{V}^{-1} \, \text{s}^{-1}) electrons and (316.46 \, \text{cm}^2 \, \text{V}^{-1} \, \text{s}^{-1}) holes respectively. To estimate the feasibility of CaV$_2$TeO$_8$ in photocatalysis, we examined the conduction and valence band edges under harsh pH conditions within PBE-GGA exchange-correlation functionals. The band edges of CaV$_2$TeO$_8$ show the halfway reaction for hydrogen evolution with reference to the Normal Hydrogen Electrode (NHE). Moreover, the Boltzmann equation interface was used to investigate the transport and thermoelectric properties. A high Seebeck coefficient in CaV$_2$TeO$_8$ at 300 K directs a thermoelectric figure of merit of 0.94.

• The paper demonstrates that CaV2TeO8 exhibits mechanical stability and a direct-indirect semiconductor behavior with a 2.8 eV bandgap, ideal for optoelectronics.
• The paper employs DFT calculations to reveal high elasticity (215.73 GPa) and low anisotropy (Zener index 1.19), supporting its potential in flexible electronic devices.
• The paper identifies promising photocatalytic activity under UV light and a competitive thermoelectric figure of merit (ZT=0.94 at 300 K) for sustainable energy conversion.

Insights into the Multifunctional Properties of CaV$_2$TeO$_8$

The paper "First-principles Investigation of CaV$_2$TeO$_8$: A Multifunctional Heteroanionic Oxychalcogenide for Photocatalytic and Thermoelectric Applications" focuses on the theoretical exploration of the orthorhombic oxytellurite compound, CaV$_2$TeO$_8$, using first-principles density functional theory (DFT) calculations. This paper explores its structural, mechanical, electronic, optical, and thermoelectric properties, aiming to address sustainability in energy conversion and photocatalytic applications.

Structural and Mechanical Characteristics

The structural analysis of CaV$_2$TeO$_8$ confirms mechanical stability, with elasticity studies revealing a high elastic modulus of 215.73 GPa. The orthorhombic crystal system's nine elastic constants, validated through the Born criteria, affirm the material's robustness. The Zener's anisotropic index of 1.19 indicates minor anisotropy, vital for potential applications in flexible electronic devices. The calculated ductile behavior, delineated by a Poisson's ratio of 0.26 and Pugh's ratio of 1.80, further emphasizes the material's capability to tolerate mechanical stresses, a crucial factor for industrial applications.

Electronic and Optical Properties

The electronic structure analysis reveals that CaV$_2$TeO$_8$ exhibits both direct and indirect electronic transitions with a significant bandgap of approximately 2.8 eV, confirming its semiconducting nature. Importantly, the calculated bandgap suggests that the material is suitable for optoelectronic applications in the UV and visible spectrum. The effective mass calculations indicate relatively high mobility for the indirect Y-Γ transition, highlighting potential advantages in processes requiring rapid charge transport.

In terms of optical properties, the absorption spectrum shows pronounced activity within the UV range, with implications for visible-light-driven photocatalytic processes. The dielectric function analyses, through both real and imaginary components, solidify its potential as a photocatalyst. These properties align well with the necessity for materials that efficiently respond to solar illumination for applications such as water splitting.

Photocatalytic Potential

For photocatalytic applications, the paper investigates redox potentials under varying pH conditions, utilizing the Normal Hydrogen Electrode (NHE) as a reference. The conduction and valence band positions suggest favorable alignments for hydrogen production, particularly in acidic environments. The robust absorption and exciton binding energy of 1812.3 meV for direct transitions indicate strong binding of photogenerated carriers, suggesting reduced recombination rates and reliable photocatalytic activity.

Thermoelectric Implications

The thermoelectric properties of CaV$_2$TeO$_8$ are discussed in terms of its Seebeck coefficient, thermal and electrical conductivity, and figure of merit (ZT). The orthorhombic oxytellurite shows a respectable ZT value of 0.94 at 300 K, underlining its candidacy for thermoelectric systems aimed at waste heat recovery. This is particularly noteworthy given the inherent complexity of achieving high ZT values in multifaceted materials like heteroanionic oxytellurides. The investigation of transport coefficients further validates the material’s potential in these energy-conversion applications.

Conclusion and Prospective Applications

The paper elucidates the multifunctional nature of CaV$_2$TeO$_8$, offering prospective advancements in both photochemical and thermoelectric fields. With a notable balance of electronic, optical, and mechanical attributes, this heteroanionic oxychalcogenide stands out as a candidate for sustainable energy technologies. Although theoretical, the insights gained from this paper provide a fundamental basis for experimental endeavors, which could substantiate these claims through real-world applications. Potential directions for future research include experimental syntheses, comprehensive pH-dependent photocatalytic efficiency studies, and prototyping of thermoelectric devices incorporating CaV$_2$TeO$_8$ to validate its practical applicability in industrial ecosystems.