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Transparent conducting oxides with p-type conductivity hold immense potential for various electronic applications. The role of native point defects in delafossite CuMO 2 (M = Al, Ga, In) as the source of p-type conductivity has been widely acknowledged. However, understanding the primary defects governing the electrical properties and devising strategies for improvement remains a critical challenge. In this study, we employ range-separated hybrid density functional calculations to elucidate the impact of acceptor defects and their interactions with hydrogen on electrical conductivity. Our findings demonstrate that hydrogen plays a pivotal role in controlling p-type conductivity in these oxides. Our investigation reveals that the interactions between hydrogen interstitial H i and copper vacancy V C u lead to the formation of stable complexes that are electrically inactive. Considerable binding energies are observed for H i – V C u complexes, indicating that they are highly bound complexes with low formation energy and, thus, high concentrations under both O-rich and O-poor conditions. A second hydrogen can be bound to V C u to form 2H i – V C u complexes, which are thermodynamically stable and function as a single donor. Furthermore, hydrogen can bind with the antisite acceptor defects, Cu M , forming H i – Cu M complexes. However, the lower binding energies associated with these complexes suggest likely dissociation into isolated H i and Cu M at relatively low temperatures. By shedding light on the strong influence of hydrogen passivation of acceptor defects, this study offers valuable insights into p-type conductivity in delafossite CuMO 2. [ABSTRACT FROM AUTHOR]

Hybrid functional calculations are presented for defects in LiGaO 2 with the fraction of non-local exchange adjusted to reproduce the recently reported exciton gap of 6.0 eV. We study how the defect transition levels of the main native defects change with respect to the band edges compared to earlier calculations which assumed a smaller bandgap near 5.1 eV. In addition, we consider defect complexes formed by combining the main native donor Ga Li with the main acceptors, V Li and Li Ga antisites as a function of their relative position. These results are used to tentatively identify the photoluminescence bands previously assigned to donor–acceptor-pair recombination. [ABSTRACT FROM AUTHOR]

Doping of the ultrawide bandgap semiconductor LiGaO 2 (E g = 5.6 eV) with N 2 , NO, and O 2 molecules placed in either Ga or Li vacancies is studied using first-principles calculations. These molecular dopants are considered potential acceptors for p -type doping. Their optimal placement and orientation relative to the lattice is studied as well as their transition levels and energy of formation. Unfortunately, they are found to have deep acceptor level transition states. We discuss the relation of the transition levels to the one-electron levels, their spin state, and defect wave functions. They are found to be closely related to those of the corresponding vacancies. [ABSTRACT FROM AUTHOR]

The pentagonal boron carbon nitride (penta-BCN) monolayer has been recently proposed as a new member of the pentagon-based two-dimensional nanosheets [Zhao et al., J. Phys. Chem. Lett. 11(9), 3501 (2020)]. By using density functional theory with the generalized gradient approximation, we have carried out detailed investigations of a hydrogenated penta-BCN sheet, where the pristine penta sheet is decorated with H atoms to the composition BCNH2. The hydrogenated penta-BCN (H-BCN) structure is mechanically, thermally, and dynamically stable. It has a wide and indirect bandgap of 4.46 eV, contrasting with the direct gap of 1.70 eV in pristine BCN. H-BCN is environmentally stable at 1 bar of H2 down to 10−10 bar; beyond this point, pristine BCN becomes more stable. Compared with penta-BCN, the components of the elastic modulus tensor C 11 and C 12 of hydrogenated penta-BCN are reduced, while C 12 and C 66 are increased. The strain tensors of piezoelectricity in H-BCN are d 21 = 0.462 , d 22 = 0.213 , and d 16 = 1.03 pm / V , which are lower than those of pristine penta-BCN. The hydrogenated BCN structure displays a higher spontaneous polarization Ps than penta-BCN (4.64 × 10−10 vs 3.38 × 10−10 C/m, respectively). The smaller in-plane Young's moduli E a and E b for H-BCN indicated that that they are softer than those for penta-BCN. Strain engineering can help tune electronic properties. In agreement with this claim, we found that the indirect gap of H-BCN was tunable from 4.46 to 3.26 eV under an applied tensile strain of 0%–16%, the range where the structure is dynamically stable throughout. Meanwhile, H-BCN is dynamically unstable under an applied compressive strain. [ABSTRACT FROM AUTHOR]

The ceramic material zinc antimony oxide ZnSb2O4 has promising electrical and magnetic properties, making it suitable for various applications such as electrochemical and energy storage. However, the effects of point defects and impurities on its electrical properties have never been revealed. Here, we employ hybrid density-functional calculations to investigate the energetics and electronic properties of native point defects and donor impurities in ZnSb2O4. The energetically favorable configurations of native point defects under selected growth conditions (O-rich and O-poor) are identified based on the calculated formation energies. The study finds no shallow donor and shallow acceptor defects with low formation energies. Still, the oxygen vacancy (VO) has the lowest formation energy among the donor-type defects under O-rich and O-poor conditions. However, it acts as a very deep acceptor, making it unlikely to provide free electron carriers to the conduction band. Moreover, electron carriers are likely to be compensated by the formation of zinc vacancies (VZn) and the zinc substituted for antimony (ZnSb), which behave as dominant acceptors. Our analysis of the charge neutrality conditions estimates that the Fermi level of undoped ZnSb2O4 would be pinned in a range that is 2.60 eV to 3.12 eV above the VBM for O-rich to O-poor growth conditions, respectively, suggesting that this material is semi-insulating. The possibility of enhancing free electron carriers by doping with Al, Ga, In, and F impurities is also investigated. Our results, however, indicate that high n-type conductivity is hindered by self-compensation in which the impurities additionally act as electron killers. Our results suggest that other impurity candidates and approaches may need to be considered to efficiently dope this material into n-type. Overall, this work paves the way for point defect engineering in this class of ternary oxides. [ABSTRACT FROM AUTHOR]

Solution‐processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short‐range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X‐ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide‐based recipe is found to contain under‐coordinated Cu atoms, pointing to the presence of SCN− vacancies. A defect passivation strategy is introduced by adding solid I2 to the processing solution. At small concentrations, the iodine is found to exist as I− which can substitute for the missing SCN− ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I2‐doped CuSCN as a p‐channel in thin‐film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I2 doping method leads to the defect‐healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance‐voltage characteristics corroborates that the trap state density is reduced upon I2 addition. [ABSTRACT FROM AUTHOR]

Researchers studying Li-ion batteries (LIBs) have become very interested in two-dimensional (2D) materials possessing an unusual pentagonal atomic structure. Recently, penta-graphene, penta-B2C, and penta-BN2 have been theoretically described. These materials are attractive for use as state-of-the-art anodes in LIBs due to their high storage capacities of 1489, 1594, and 2071 mA h g−1, respectively. Here, we propose enhancing storage capacity by introducing defect doping. For example, one Al atom was incorporated into 2 × 2 penta-BN2, corresponding to AlB7N16. The energy calculated for the adsorption of a single Li atom onto the Al-doped material is more favorable than that for the Al-free analog, indicating that doping can strengthen an affinity for Li. The Al-doped penta-BN2 exhibits metallic conductivity during Li adsorption. In the layer-by-layer Li adsorption, doping a single Al atom into 2 × 2 penta-BN2 has an 11% higher storage capacity (2297 mA h g−1) than penta-BN2 despite having a slightly heavier formula weight. The Al-doped penta-BN2 displays a low open-circuit voltage of 0.48 V. Substituting aluminum for boron enhances the Li adsorption capacity of penta-BN2, and the computed storage capacity is presently one of the highest published values for pentagonal materials. [ABSTRACT FROM AUTHOR]

The native point defects are studied in LiGaO 2 using hybrid functional calculations. We find that the relative energy of formation of the cation vacancies and the cation antisite defects depends strongly on the chemical potential conditions. The lowest energy defect is found to be the Ga Li 2 + donor. It is compensated mostly by V Li − 1 and in part by Li Ga − 2 in the more Li-rich conditions. The equilibrium carrier concentrations are found to be negligible because the Fermi level is pinned deep in the gap and this is consistent with insulating behavior in pure LiGaO 2. V Ga has high energy under all reasonable conditions. Both Ga Li and V O are found to be negative U centers with deep 2 + / 0 transition levels. [ABSTRACT FROM AUTHOR]

The native point defects are studied in LiGaO 2 using hybrid functional calculations. We find that the relative energy of formation of the cation vacancies and the cation antisite defects depends strongly on the chemical potential conditions. The lowest energy defect is found to be the Ga Li 2 + donor. It is compensated mostly by V Li − 1 and in part by Li Ga − 2 in the more Li-rich conditions. The equilibrium carrier concentrations are found to be negligible because the Fermi level is pinned deep in the gap and this is consistent with insulating behavior in pure LiGaO 2. V Ga has high energy under all reasonable conditions. Both Ga Li and V O are found to be negative U centers with deep 2 + / 0 transition levels. [ABSTRACT FROM AUTHOR]

Most transparent conducting oxides (TCOs) exhibit n-type conductivity and are difficult to dope into p-type. Therefore, the development of efficient p-type TCOs is challenging. ZnRh2O4 spinel has been recognized as a potential p-type TCOs. However, the source of its p-type conductivity has not been elucidated. In this study, we used hybrid density functional calculations to investigate the energetics and electronic properties of native defects in ZnRh2O4, including vacancies, interstitials, and cation antisites. We found that all acceptor-type defects including Zn vacancies, Zn antisites, and Rh vacancies acted as deep centers. Charge neutrality analysis suggested that undoped ZnRh2O4 may behave as a p-type semiconductor with hole concentrations of 1018–1019 cm−3 under the extreme O-rich/Rh-poor growth condition in which ZnRh has a low formation energy and acts as the major source of hole carriers. However, under realistic growth conditions, the experimentally determined hole concentration significantly exceeds that which is calculated. Our results suggest that native point defects are unlikely to be responsible for the high hole concentrations observed in ZnRh2O4 spinel. [ABSTRACT FROM AUTHOR]

For over a century, lead dioxide (PbO2) has been investigated in lead–acid batteries and extensively utilized in a variety of applications. Identifying the surface properties and equilibrium morphology of β-PbO2 (rutile phase) particles is mandatory for industrial utilization and surface engineering. Using density-functional calculations within the generalized gradient approximation revised for solids (PBEsol), we investigate a variety of surface properties of β-PbO2. The surface energies of low-Miller-index stoichiometric surfaces are firstly determined, and the (110) surface is found to be the most thermodynamically stable. The relative energetics of these surfaces are represented by a Wulff construction which shows an acicular shape, mostly dominated by the (110) and (100) surfaces. Besides, we investigate the surface chemistry of β-PbO2 under reduction and oxidation conditions as a function of oxygen pressure, finding that most surfaces except for (100) and (110) are likely to be oxidized. Under oxygen pressure at 1 atm and oxygen-rich limit, the (101) surface is the most thermodynamically stable, dominating the Wulff construction with pyramidal shapes. Our results indicate that the growth conditions that cause non-stoichiometry of the surface could modify the equilibrium Wulff shape of β-PbO2. Our predicted Wulff shapes and dominant facets agree with the experimental results in which the pyramidal shape of the β-PbO2 grains has often been observed with the (101) preferred orientation. [ABSTRACT FROM AUTHOR]

Oxygen vacancy defects (VO) in Ti-based oxides play important roles in catalytic processes despite limited knowledge regarding their formation and characterization. Here, we demonstrate the use of X-ray absorption spectroscopy (XAS) measurements to compare the relative proportion of VO defects in as-grown alkali hexatitanate A2Ti6O13 (A = Li, Na, K). Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions were studied. The similarity of measured XANES spectra of Ti K-edge in all samples indicates the presence of (Ti4+)O6 units in good agreement with reported X-ray diffraction results. The small influence of cations A at the tunnel was observed and can be well reproduced in the simulated spectra. In addition, we present a semi-quantitative approach to intuitively determine the content of VO defects in oxygen-deficient K2Ti6O13-x by in situ time-resolved XAS measurements under reducing conditions (10%H2/Ar, 50-650 °C). The in situ XANES measurements indicate that the oxidation state of bulk Ti remains the same as the as-grown sample, i.e., 4+, at elevated temperatures. By in situ EXAFS measurements, the relative number of VO defects is highest at a reduction temperature of ∼550 °C and slightly decreases after that. To confirm the formation of VO defects, first-principles calculations were independently carried out using a 126-atom K2Ti6O13 supercell with VO at various positions. Based on calculated EXAFS, the removal of the oxygen atom nearest to the tunnel, which is the lowest energy structure, provides a good match to the experimental spectra. [ABSTRACT FROM AUTHOR]

Recently, the C2N monolayer with an optical bandgap of 1.96 eV has emerged as a novel two-dimensional material for modern optoelectronic devices. Herein, we report its bandgap modulation by using a simple bilayer formation that includes the application of an electric field and strain. We identify four energetically favorable bilayer configurations (AA-, AB-, AB′-, and Min-stacking) by using a hybrid functional, obtaining a calculated bandgap of 1.3–1.6 eV. When subjected to a perpendicular electric field up to 4 V/nm, the bandgap decreases by as much as 0.5 eV, which correlates with the increasing energy of the valence-band maximum, where the N-px and N-py states shift closer to the N-pz state. Without the electric field, the bandgap decreases when the interlayer distance is contracted by a compressive strain. We express the strain (or interlayer distance) and the physical applied pressure via the stabilized jellium equation of state. For the Min-stacking configuration, the bandgap decreases from 1.75 to 0.9 eV upon applying a pressure of 35 GPa. The strain-induced reduction in the bandgap is similarly monitored under an applied electric field. Our theoretical work suggests that the electric field and strain (or applied pressure) can be used to tune the electronic properties of the bilayer C2N. [ABSTRACT FROM AUTHOR]

A first principles study of Mn impurity in PbTi[O.sub.3] and PbZr[O.sub.3] is conducted to determine its favorable location and its electronic and magnetic properties. The results show that it is energetically favorable for the Mn atom to substitute for Ti/Zr under all equilibrium crystal growth conditions.