The Electronic, Structural, and Optical Properties of CaNb₂O₆ Compound: Theoretical Study

Abstract

Based on the density functional theory (DFT) as incorporated in the Wien2k package, the lattice parameters and atomic position of calcium niobate (CaNb2O6) were optimized. Furthermore, the electronic, optical, and structural properties of the relaxed compound were calculated. Relaxed calcium niobate presents a direct band gap with 3.5 eV, which makes it a good candidate for photovoltaic applications. The DFT calculation reveals that the O atoms make the major contributions in the valence band, while Nb and Ca atoms are the dominant contributors in lower and upper portions of the conduction band, respectively. Moreover, the optical properties of compounds such as refractivity, dielectric constant, reflectivity, etc. are calculated and discussed in detail.

Low‐Symmetry 2D Perovskite CaNb2O6 for Polarization‐Sensitive UV Photodetection

“…The in-plane anisotropy of optical absorption properties in CaNb 2 O 6 nanosheet can be well explained by considering the discrepancy of refractive index in CaNb 2 O 6 along different crystalline orientations. [22,23] The merits of CaNb device shows photoresponse at specially selected wavelengths, ranging from near-UV (400 nm) to solar-blind UV (280 nm) light (Figure 4b). Under 375 nm illumination, the device shows extremely low dark current as well as pronounced photocurrent, and the transient photoresponse (I ds -t) of device was also recorded (Figure 4c and Figure S10a, Supporting Information).…”

“…These layers are then stacked vertically along the a ‐axis direction with Ca 2+ sandwiched between them. [ 22 ] The strong interfacial coupling effect between stacked layers in CaNb 2 O 6 crystal poses a great challenge for the isolation of large‐area nanosheets with planar structure. To minimize the thickness, a space‐confined chemical vapor transport (CVT) strategy was employed for the preparation of CaNb 2 O 6 nanosheets.…”

“…The relaxed CaNb 2 O 6 crystal presents a direct band gap with 3.85 eV, consistent with previous reports. [ 22 ] Figure S6 (Supporting Information) plots the micro‐absorption spectrum of an as‐grown CaNb 2 O 6 nanosheet with thickness about 10 nm, showing an obvious absorption edge around 310 nm. Thus, an optical bandgap up to 4.1 eV can be determined.…”

“…The in‐plane anisotropy of optical absorption properties in CaNb 2 O 6 nanosheet can be well explained by considering the discrepancy of refractive index in CaNb 2 O 6 along different crystalline orientations. [ 22,23 ]…”

“…[ 21 ] Calcium niobate (CaNb 2 O 6 ), which belongs to sub‐component of the complex perovskite family A(B′ 1/3 B″ 2/3 )O 3 , has attracted significant attentions as laser host due to its strong light–matter couple effect in UV region. [ 22,23 ] It possesses a wide bandgap ( E g ) and presents asymmetrical atomic structure raised from the distortions and orientations of the oxygen octahedra. [ 24 ] Therefore, a high anisotropy of physical properties in CaNb 2 O 6 nanosheets can be expected, and it might be an ideal candidate for designing polarization‐sensitive photodetectors.…”