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DOE OSTI2025

Tracking oxygen vacancy migration in memristor devices using operando hard X-ray photoelectron spectroscopy

Fabrication of ultrathin (sub-2 nm) oxide semiconductor memristors poses the fundamental challenge of achieving oxide growth with atomic precision in terms of electronic structure and defect formation. Recently, ultrathin memristors consisting of bilayers of mixed Al 2 O 3 and MgO atomic layers were fabricated using an in vacuo atomic layer deposition process. This approach offers a unique platform for precise atomic control of oxygen vacancies in the device in which the vacancies are introduced by placing MgO atomic layers between pristine Al 2 O 3 layers. In this work, we present a systematic operando Hard X-ray PhotoElectron Spectroscopy (HAXPES) study of the switching of such memristors, combined with complementary current-voltage and capacitance-voltage (C-V) measurements. We used a memristor stack of Al 2 O 3 /MgO atomic layers, with the MgO-containing oxide deposited on the bottom Al metal electrode and a pure Al 2 O 3 layer below the top Pd electrode. HAXPES analysis shows a substantial change in the chemical shift of the Aluminum oxide when switching between the ”OFF” and ”ON” states indicative of a redistribution of oxygen vacancies in the device active layer. Interestingly, subsequent switching to the OFF state shows hysteretic behavior indicating the retention of some oxygen vacancies in the top Al 2 O 3 layer. This vacancy retention can be correlated with the stochastic behavior of the switching voltage observed in these devices. C–V measurements show a clear frequency-dependent response in the OFF state, consistent with enhanced polarization and vacancy trapping at low frequencies.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Local electric field measurement in GaN diodes by exciton Franz–Keldysh photocurrent spectroscopy

The eXciton Franz–Keldysh (XFK) effect is observed in GaN p–n junction diodes via the spectral variation of photocurrent responsivity data that redshift and broaden with increasing reverse bias. Photocurrent spectra are quantitatively fit over a broad photon energy range to an XFK model using only a single fit parameter that determines the line shape and the local bias (V l ), uniquely determining the local electric field maximum and depletion widths. As expected, the spectrally determined values of V l vary linearly with the applied bias (V) and reveal a large reduction in the local electric field due to electrostatic non-uniformity. The built-in bias (V bi ) is estimated by extrapolating V l at V=0, which, when compared with independent C-V measurements, indicates an overall ±0.31 V accuracy of V l . This demonstrates sub-bandgap photocurrent spectroscopy as a local probe of electric field in wide bandgap diodes that can be used to map out regions of device breakdown (hot spots) for improving electrostatic design of high-voltage devices.

42 ENGINEERING↗

DOE OSTI2021

Impact of high-dose gamma-ray irradiation on electrical characteristics of N-polar and Ga-polar GaN p–n diodes

We investigate the impact of high-dose gamma-ray irradiation on the electrical performance of Ga-polar and N-polar GaN-based p-n diodes grown by metalorganic chemical vapor deposition. We compare the current density-voltage (J-V), capacitance-voltage (C-V), and circular transfer length method (CTLM) characteristics of the p-n diodes fabricated on Ga-polar and N-polar orientations before and after irradiation. The relative turn-on voltage increases for the Ga-polar diodes with increasing irradiation dose, while it increases initially and then starts to decrease for the N-polar diodes. The p-contact total resistance increases for Ga-polar and decreases for N-polar samples, which we attribute to the formation of point defects and additional Mg activation after irradiation. The J-V characteristics of most of the tested diodes recovered over time, suggesting the changes in the J-V characteristics are temporary and potentially due to metastable occupancy of traps after irradiation. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) measurements reveal the existence of different types of initial defects and surface electronic states on Ga-polar and N-polar samples. Gallium vacancies (V Ga ) are dominant defects in Ga-polar samples, while nitrogen vacancies (V N ) are dominant in N-polar samples. The presence of a higher concentration of surface states on Ga-polar surfaces compared to N-polar was confirmed by calculating the band bending and the corresponding screening effect due to opposite polarization bound charge and ionized acceptors at the surface. The difference in surface stoichiometry in these two orientations is responsible for the different behavior in electrical characteristics after gamma-ray interactions.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Identification of the defect dominating high temperature reverse leakage current in vertical GaN power diodes through deep level transient spectroscopy

Deep level defects in wide bandgap semiconductors, whose response times are in the range of power converter switching times, can have a significant effect on converter efficiency. We use Deep Level Transient Spectroscopy (DLTS) to evaluate such defect levels in the n- drift layer of vertical GaN (v-GaN) power diodes with VBD ~ 1500 V. DLTS reveals three energy levels that are at ~0.6 eV (highest density), ~0.27 eV (lowest density) and ~ 45 meV (a dopant level) from the conduction band. Dopant extraction from Capacitance-Voltage measurement test (C-V) at multiple temperatures enables trap density evaluation, and the ~0.6 eV trap has a density of 1.2 × 10 15 cm -3 . Here, the 0.6 eV energy level and its density are similar to a defect that is known to cause current collapse in GaN based surface conducting devices (like HEMTs). Analysis of reverse bias currents over temperature in the v-GaN diodes indicates a predominant role of the same defect in determining reverse leakage current at high temperatures, reducing switching efficiency.

42 ENGINEERING↗

DOE OSTI2020

Growth and characterization of homoepitaxial β-Ga 2 O 3 layers

ß-Ga 2 O 3 is a next-generation ultra-wide bandgap semiconductor (E g = 4.8 eV to 4.9 eV) that can be homoepitaxially grown on commercial substrates, enabling next-generation power electronic devices among other important applications. Analyzing the quality of deposited homoepitaxial layers used in such devices is challenging, in part due to the large probing depth in traditional x-ray diffraction (XRD) and also due to the surface-sensitive nature of atomic force microscopy (AFM). Here, a combination of evanescent grazing-incidence skew asymmetric XRD and AFM are investigated as an approach to effectively characterize the quality of homoepitaxial ß-Ga 2 O 3 layers grown by molecular beam epitaxy at a variety of Ga/O flux ratios. Accounting for both structure and morphology, optimal films are achieved at a Ga/O ratio of ~1.15, a conclusion that would not be possible to achieve by either XRD or AFM methods alone. Finally, fabricated Schottky barrier diodes with thicker homoepitaxial layers are characterized by J-V and C-V measurements, revealing an unintentional doping density of 4.3×10 16 cm -3 - 2×10 17 cm -3 in the epilayer. These results demonstrate the importance of complementary measurement methods for improving the quality of the ß-Ga 2 O 3 homoepitaxial layers used in power electronic and other devices.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Impact of proton irradiation on 4H-SiC Low Gain Avalanche Detectors (LGADs)

Silicon carbide (SiC) particle detectors have the potential to provide time resolutions and robust performance in extreme environments which exceed that of silicon detectors. In this work 4H-SiC low gain avalanche detectors (LGADs) and complementary PiN diodes were irradiated with 2.5 GeV protons at fluences up to 3.33 × 10 14 p/cm 2 . The electrostatic performance of both irradiated and non-irradiated devices was evaluated using I-V and C-V measurements. Moreover, charge collection measurements using α particles were also conducted. SiC LGADs displayed a loss in rectification, high ON-state resistances >10 10 Ω-cm 2 , and the complete removal of gain when exposed to the highest proton fluence. Additionally, the reductions in capacitance and OFF-state current pointed to compensation of the gain layer as a gain reducing mechanism. The introduction of radiation-induced defects also hinders carrier acceleration, which reduces impact ionization and further gain reduction. LGADs exposed to a fluence of 1 × 10 14 p/cm 2 experienced a partial recovery in gain (originally having a value of ∼ 2) with a value of ∼ 1.65 when applying a bias of 500 V. Charge trapping was also seen in the reduction of charge collection efficiency (CCE) to ∼ 65% for the PiN diode. However, despite the reduction in device performance, the demonstration of a measurable signal after irradiation points to the potential of SiC LGAD detectors for future high energy physics applications.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Impacts of Non-Ideal Back Contact on Capacitance Measurements in CdTe Solar Cells

CdTe solar cells suffer from a non-ideal back contact which can strongly affect the equivalent circuit model and complicate capacitance measurements. Here, five different back contact materials are deposited on identical CdTe absorbers and their influence on capacitance measurements is characterized. A five-element equivalent circuit model is shown to represent a CdTe solar cell with a non-ideal back contact, and capacitance-frequency (C-f) measurements on each sample clearly show the influence of this contact. Capacitance-voltage (C-V) measurements on each sample show the influence of frequency on measured capacitance. In the AlGaOx/Au sample, temperature dependent C-fs show the back barrier height to be 240 meV, and ongoing measurements will give a comparison of back barrier heights for all samples. This study provides insight into the efficacy of various back contacts and highlights potential errors in the interpretation of capacitance measurements due to the presence of the back contact.

cadmium compounds↗

DOE OSTI2022

Investigation of Ga 2 O 3 as a new transparent conductive oxide for photovoltaics applications

This small innovation project intended to leverage recent activity and advances in ultrawide-bandgap oxide power electronics toward the investigation of Ga 2 O 3 as a transparent conductive oxide (TCO) for use in photovoltaics (PV). Ga 2 O 3 ’s theoretical advantage over incumbent TCOs is its very large bandgap of 4.8 eV, ensuring optical transparency of photons with λ ≥ 260 nm, effectively the full terrestrial solar spectrum. At the time of proposal writing, literature on Ga 2 O 3 as a TCO/optical material was relatively sparse — what little existed was focused on for UV sensors and/or emitters, with none related to PV. As such, this project was intended to help determine the potential of Ga 2 O 3 as a PV-oriented TCO by investigating its deposition using tools common to the PV and electronics industries — atomic layer deposition (ALD) and RF sputtering (RS), both of which are already used in PV manufacturing — and its resultant optical and electronic properties. Final project goals were to test its application to Si and III-V solar cells. Controllable film thickness and excellent uniformity was established for both methods deposition methods, with ALD providing higher precision for thinner films and RS more effective for growing thicker films. The as-deposited films were found to be amorphous in nature. Spectroscopic ellipsometry (SE) confirmed bandgaps of at least 4.8 eV and non-parasitic absorption across both AM0 and AM1.5G spectra; a refractive index approaching the expected value of 1.8 was also observed, with some degree of tunability based on process parameters. Using this initial optical data, a transfer matrix model, which interfaces with in-house EQE and LIV models, was developed to simulate Ga 2 O 3 optical effects on various solar cells, included potential in antireflection coatings (ARCs). Despite promising optical properties, the resultant resistivity / conductivity metrics did not meet expectations, regardless of deposition process. Although thick RS-deposited films, using both undoped and 1 at% Ge (n-type) doped sintered targets — demonstrated high net carrier concentrations (via C-V), and low specific resistance Ohmic contacts were demonstrated, transmission line measurements (TLM) showed very high resistivity. Further analysis indicated high vertical film conductivity, but very low lateral conductivity. Deeper characterization revealed a relatively high density of nano/microcrystalline inclusions that were ostensibly the source of the vertical conductivity, with the amorphous matrix serving as an effective insulator (likely due to high concentrations of electronic trap states). Despite extensive work to increase film polycrystallinity — demonstrated via high temperature annealing — sufficient lateral conductivity for TCO use was not achieved. The final phase of the project shifted focus toward investigation of ALD-deposited Ga 2 O 3 ’s potential as a passivant and/or passivating contact for both Si and III-V solar cells, with expectation of performance similar to Al 2 O 3 . However, initial rounds of testing using our baseline ALD process yielded minimal (but not quite zero) passivation of both GaInP and Si surfaces. Dielectric passivation is well-known to be highly process sensitive; given the unoptimized nature of the process used, this work was deemed inconclusive. The final outlook with respect to feasibility of Ga 2 O 3 as a PV-oriented TCO is, ultimately, still uncertain. The work performed in this project confirmed the optical properties and deposition methods, but the achieved electrical properties do not meet technological needs; literature reports in recent years are somewhat inconsistent and potentially untrustworthy, but generally appear to be in line with our results. At the very least it is clear that, should Ga 2 O 3 still be under consideration for PV TCO and/or selective contact applications, a significant amount of optimization and study is still needed.

14 SOLAR ENERGY↗

DOE OSTI2025

Fabrication of 4H-SiC Low Gain Avalanche Detectors (LGADs)

Low gain avalanche detectors (LGADs) offer high temporal resolution for high energy particle detection, which is critical for next generation experiments in hadron colliders. While silicon LGADs (Si-LGADs) have rapidly matured in the last decade, research into silicon carbide (SiC) LGADs has only recently begun. By accounting for fundamental differences in material properties and fabrication processes, we present a prototype device design and process flow for 4H-SiC LGADs with etch-based isolation. Critical steps of the process flow and their results are discussed, including plasma etching, passivation, and the formation of low resistivity contacts. Electrical characterization (I-V, C-V) shows sufficient depletion of the device structure to demonstrate low-gain charge carrier multiplication.

High Energy Physics↗

DOE OSTI2024

Impacts of Non-Ideal Back Contact on Capacitance Measurements in CdTe Solar Cells

14 SOLAR ENERGY↗

DOE OSTI2020

Experimental Study of Acceptor Removal in UFSD

The performance of the Ultra-Fast Silicon Detectors (UFSD) after irradiation with neutrons and protons is compromised by the removal of acceptors in the thin layer below the junction responsible for the gain. In this study, the effect is tested both with capacitance–voltage, C–V, measurements of the doping concentration and with measurements of charge collection, CC, using charged particles. We find a perfect linear correlation between the bias voltage to deplete the gain layer determined with C–V and the bias voltage to collect a defined charge, measured with charge collection. An example for the usefulness of this correlation is presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Materials Data on V2C by Materials Project

V2C is beta Vanadium nitride-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. V2+ is bonded in a distorted trigonal planar geometry to three equivalent C4- atoms. There are a spread of V–C bond distances ranging from 2.01–2.04 Å. C4- is bonded to six equivalent V2+ atoms to form a mixture of corner and edge-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 50–51°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on V6C5 by Materials Project

V6C5 crystallizes in the trigonal P3_112 space group. The structure is three-dimensional. there are three inequivalent V+3.33+ sites. In the first V+3.33+ site, V+3.33+ is bonded to five C4- atoms to form a mixture of edge and corner-sharing VC5 square pyramids. There are a spread of V–C bond distances ranging from 1.97–2.13 Å. In the second V+3.33+ site, V+3.33+ is bonded to five C4- atoms to form a mixture of edge and corner-sharing VC5 square pyramids. There are a spread of V–C bond distances ranging from 1.98–2.13 Å. In the third V+3.33+ site, V+3.33+ is bonded to five C4- atoms to form a mixture of edge and corner-sharing VC5 square pyramids. There are a spread of V–C bond distances ranging from 1.92–2.09 Å. There are five inequivalent C4- sites. In the first C4- site, C4- is bonded to six V+3.33+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 8–9°. In the second C4- site, C4- is bonded to six V+3.33+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedral tilt angles are 7°. In the third C4- site, C4- is bonded to six V+3.33+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 8–9°. In the fourth C4- site, C4- is bonded to six V+3.33+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 7–9°. In the fifth C4- site, C4- is bonded to six V+3.33+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 7–9°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on V8C7 by Materials Project

V8C7 crystallizes in the cubic P4_332 space group. The structure is three-dimensional. there are two inequivalent V+3.50+ sites. In the first V+3.50+ site, V+3.50+ is bonded to six C4- atoms to form VC6 octahedra that share corners with six equivalent VC5 square pyramids, edges with three equivalent VC6 octahedra, and edges with nine equivalent VC5 square pyramids. There are three shorter (2.07 Å) and three longer (2.14 Å) V–C bond lengths. In the second V+3.50+ site, V+3.50+ is bonded to five C4- atoms to form VC5 square pyramids that share corners with two equivalent VC6 octahedra, corners with seven equivalent VC5 square pyramids, edges with three equivalent VC6 octahedra, and edges with five equivalent VC5 square pyramids. The corner-sharing octahedra tilt angles range from 5–7°. There are a spread of V–C bond distances ranging from 1.92–2.11 Å. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to six equivalent V+3.50+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedral tilt angles are 9°. In the second C4- site, C4- is bonded to six V+3.50+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 3–10°. In the third C4- site, C4- is bonded to six V+3.50+ atoms to form a mixture of edge and corner-sharing CV6 octahedra. The corner-sharing octahedra tilt angles range from 3–10°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on V2C by Materials Project

V2C is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one V2C sheet oriented in the (0, 0, 1) direction. V2+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All V–C bond lengths are 2.03 Å. C4- is bonded to six equivalent V2+ atoms to form edge-sharing CV6 octahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on V4C3 by Materials Project

V4C3 is MAX Phase-derived structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three V4C3 sheets oriented in the (0, 0, 1) direction. there are two inequivalent V3+ sites. In the first V3+ site, V3+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing VC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All V–C bond lengths are 2.09 Å. In the second V3+ site, V3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All V–C bond lengths are 1.99 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to six V3+ atoms to form a mixture of corner and edge-sharing CV6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to six equivalent V3+ atoms to form a mixture of corner and edge-sharing CV6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on VC3 by Materials Project

C3V crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent V4+ sites. In the first V4+ site, V4+ is bonded in a 1-coordinate geometry to ten C+1.33- atoms. There are a spread of V–C bond distances ranging from 2.14–2.80 Å. In the second V4+ site, V4+ is bonded in a 7-coordinate geometry to seven C+1.33- atoms. There are a spread of V–C bond distances ranging from 1.98–2.28 Å. In the third V4+ site, V4+ is bonded in a 5-coordinate geometry to six C+1.33- atoms. There are a spread of V–C bond distances ranging from 2.00–2.75 Å. In the fourth V4+ site, V4+ is bonded in a 6-coordinate geometry to eight C+1.33- atoms. There are a spread of V–C bond distances ranging from 2.10–2.55 Å. In the fifth V4+ site, V4+ is bonded in a 8-coordinate geometry to eight C+1.33- atoms. There are a spread of V–C bond distances ranging from 1.96–2.48 Å. In the sixth V4+ site, V4+ is bonded in a 8-coordinate geometry to eight C+1.33- atoms. There are a spread of V–C bond distances ranging from 2.01–2.47 Å. In the seventh V4+ site, V4+ is bonded in a 6-coordinate geometry to seven C+1.33- atoms. There are a spread of V–C bond distances ranging from 1.95–2.63 Å. In the eighth V4+ site, V4+ is bonded in a 9-coordinate geometry to nine C+1.33- atoms. There are a spread of V–C bond distances ranging from 1.99–2.43 Å. There are twenty-four inequivalent C+1.33- sites. In the first C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. There is one shorter (1.42 Å) and one longer (1.48 Å) C–C bond length. In the second C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. There is one shorter (1.48 Å) and one longer (1.49 Å) C–C bond length. In the third C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to four V4+ and one C+1.33- atom. The C–C bond length is 1.44 Å. In the fourth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to four V4+ and one C+1.33- atom. The C–C bond length is 1.41 Å. In the fifth C+1.33- site, C+1.33- is bonded in a 4-coordinate geometry to two V4+ and two C+1.33- atoms. There is one shorter (1.41 Å) and one longer (1.47 Å) C–C bond length. In the sixth C+1.33- site, C+1.33- is bonded in a 4-coordinate geometry to one V4+ and three C+1.33- atoms. There are a spread of C–C bond distances ranging from 1.42–1.47 Å. In the seventh C+1.33- site, C+1.33- is bonded in a 3-coordinate geometry to one V4+ and three C+1.33- atoms. Both C–C bond lengths are 1.46 Å. In the eighth C+1.33- site, C+1.33- is bonded in a 3-coordinate geometry to one V4+ and three C+1.33- atoms. There is one shorter (1.44 Å) and one longer (1.48 Å) C–C bond length. In the ninth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. The C–C bond length is 1.49 Å. In the tenth C+1.33- site, C+1.33- is bonded in a distorted pentagonal planar geometry to three V4+ and two C+1.33- atoms. In the eleventh C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to two V4+ and three C+1.33- atoms. There are a spread of C–C bond distances ranging from 1.44–1.57 Å. In the twelfth C+1.33- site, C+1.33- is bonded in a distorted trigonal pyramidal geometry to two V4+ and two C+1.33- atoms. The C–C bond length is 1.44 Å. In the thirteenth C+1.33- site, C+1.33- is bonded in a 7-coordinate geometry to five V4+ and two C+1.33- atoms. The C–C bond length is 1.50 Å. In the fourteenth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. The C–C bond length is 1.46 Å. In the fifteenth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. The C–C bond length is 1.46 Å. In the sixteenth C+1.33- site, C+1.33- is bonded in a 4-coordinate geometry to two V4+ and two C+1.33- atoms. The C–C bond length is 1.43 Å. In the seventeenth C+1.33- site, C+1.33- is bonded in a 6-coordinate geometry to four V4+ and two C+1.33- atoms. The C–C bond length is 1.43 Å. In the eighteenth C+1.33- site, C+1.33- is bonded in a 3-coordinate geometry to three V4+ and two C+1.33- atoms. In the nineteenth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to two V4+ and three C+1.33- atoms. The C–C bond length is 1.52 Å. In the twentieth C+1.33- site, C+1.33- is bonded in a 5-coordinate geometry to three V4+ and two C+1.33- atoms. In the twenty-first C+1.33- site, C+1.33- is bonded in a 3-coordinate geometry to two V4+ and three C+1.33- atoms. In the twenty-second C+1.33- site, C+1.33- is bonded in a 4-coordinate geometry to one V4+ and three C+1.33- atoms. In the twenty-third C+1.33- site, C+1.33- is bonded in a 1-coordinate geometry to four V4+ and one C+1.33- atom. In the twenty-fourth C+1.33- site, C+1.33- is bonded in a 4-coordinate geometry to two V4+ and two C+1.33- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on V2C by Materials Project

V2C crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two V2C sheets oriented in the (0, 0, 1) direction. V2+ is bonded in a 3-coordinate geometry to three equivalent C4- atoms. All V–C bond lengths are 2.02 Å. C4- is bonded to six equivalent V2+ atoms to form edge-sharing CV6 octahedra.

36 MATERIALS SCIENCE↗