Search NASA⌕ Search

SEARCH · Search NASA

Results for “wurtzite”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A room temperature polar magnetic metal

The emergence of long-range magnetic order in noncentrosymmetric compounds has stimulated interest in the possibility of exotic spin transport phenomena and topologically protected spin textures for applications in next-generation spintronics. Polar magnets, with broken symmetries of spatial inversion and time reversal, usually host chiral spin textures. This work reports on a wurtzite-structure polar magnetic metal, identified as AA'-stacked (Fe 0.5 Co 0.5 ) 5 GeTe 2 , which exhibits a Néel-type skyrmion lattice as well as a Rashba-Edelstein effect at room temperature. Atomic resolution imaging of the structure reveals a structural transition as a function of Co-substitution, leading to the emergence of the polar phase at 50% Co. We report this discovery reveals an unprecedented layered polar magnetic system for investigating intriguing spin topologies, and it ushers in a promising new framework for spintronics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Native and radiation induced point defects in AlN and Sc-doped AlN

Herein, we have performed first-principles calculations to investigate the electronic structure, configurations, formation, and binding energies of native and radiation induced point defects in pristine and Sc-doped wurtzite AlN. For the native defects, the nitrogen vacancy has the lowest formation energy in p-type material while the aluminum vacancy has the lowest formation energy in n-type material which is consistent with the previous studies. Several interstitial defect structures were modeled for Al, N, and Sc atoms. The effects of charge state on their relative stability were investigated. The binding energy of Sc with point defects was calculated and found to be dependent strongly on the defect type and charge state. The results obtained are discussed in light of the possible Sc effects on the radiation damage evolution in AlN. Thus the attraction of Sc atom to N vacancy and both Al and N interstitials reduces their mobility and increases Frenkel pair recombination distance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electronic and optical properties of transition metal impurities in GaN and AlN

The optical properties of Cr(III) impurities are well studied and exploited in 𝛼−Al 2 ⁢O 3 , which enables ruby lasers. Photoluminescence spectra resembling the famous 1.78 eV emission of Cr in 𝛼−Al 2 ⁢O 3 have been observed in other wide-band-gap host materials, in particular AlN. However, it is unclear whether Cr would produce the same emission in the nitrides as in 𝛼−Al 2 ⁢O 3 , especially given the different local environment (tetrahedral vs octahedral coordination). We investigate the electronic and optical properties of transition metal substitutional impurities (Cr, Co, Ni, and Cu) in wurtzite GaN and AlN from first principles, utilizing hybrid density functional theory. We calculate the optical transition energies using a constrained occupation approach that accounts for the multideterminant nature of the excited states. Our results indicate that substitutional Cr(III) is not responsible for the emission near 1.78 eV observed in the nitrides. Among the examined impurities, only substitutional Co(II) produces emission near 1.78 eV. Based on the favorable properties of Co(II) (low formation energy, small Huang-Rhys factor, and an 𝑆 = 3/2 ground state) we propose it as a promising single-photon emitter or spin qubit. We additionally assign the PL peak observed near 1.05 eV in GaN and AlN to the 2 𝐸→ 4 𝐴 2 transition of the Ni(III) substitution.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Aluminum Boron Nitride Ferroelectric Field-Effect Transistors With ZnO Semiconductor Channel

The discovery of ferroelectricity in hafnium zirconium oxide (HfxZr 1−x O2) and related fluorite materials has spurred interest in ferroelectric devices suitable for integration with silicon integrated circuits (ICs), especially those that can be embedded in the back-end-of-line (BEOL) process. More recently, ferroelectricity has been found in wurtzite aluminum nitride-based materials, such as scandium and boron-doped aluminum nitride (Al 1−x ScxN and Al 1−x BxN). Although these materials currently have undesirably large coercive electric fields, and small breakdown electric field-to-coercive electric field ratio, their low processing temperatures and large remanent polarization offer intriguing possibilities for device applications. Furthermore, we report ferroelectric field-effect transistors (FeFETs) with a 15 nm thick Al0.88B0.12N layer and an 11 nm ZnO semiconductor channel, achieving a memory window >1 V and switching voltages ( V switch ) <±10 V.

42 ENGINEERING↗
DOE OSTI2023

Phase evolution during conventional and reactive flash sintering of (Mg,Ni,Co,Cu,Zn)O via in situ X-ray diffraction

Reactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X-ray diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy-stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate-controlled mode. The same reaction pathway is verified in both instances: the starting rock-salt (RS), spinel (Co 3 O 4 ), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single-phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). Furthermore, in RFS, the single-phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm -2 /min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Synergistic effects of Al, Ga, and In doping on ZnO nanorod arrays grown via citrate-assisted hydrothermal technique for highly efficient and fast scintillator screens

To be used as efficient alpha particle scintillator in the fields of nuclear security, nuclear nonproliferation and high-energy physics, scintillator screens must have high light output and fast decay properties. While there has been a great deal of progress in scintillation efficiency, achieving fast decay time properties are still a challenge. In this work, the near band edge (NBE) UV luminescence and alpha particle induced scintillation properties of vertically aligned densely packed ZnO nanorods (NRs) doped with Al, Ga, and In have been thoroughly investigated. The high crystalline hexagonal wurtzite structure with a strong orientation through the c -axis plane (002) and aspect ratios in the range 13–22 have been observed for all ZnO NRs. Electron paramagnetic resonance (EPR) analysis exhibited paramagnetic signals at g ≈ 1.96 for all ZnO NRs. A cost effective green hydrothermal synthesis technique was employed to grow well-aligned NRs. Using citrate as an additive acting as a strong reducing agent in the solution during the crystal growth, defects on the surface are significantly suppressed, thereby enhancing the NBE UV emission. Significantly higher NBE UV emission was observed from the top surface of ZnO NRs in cathodoluminescence (CL) microscopy. Results show that citrate assisted donor doping of ZnO NRs not only reduces the defect emission and NBE self-absorption, but also induces fast decay time (~ 600–700 ps), which makes ZnO NRs a good candidate for fast alpha particle scintillator screens used in associated particle imaging for time and direction tagging of individual neutrons generated in D–T and D–D neutron generators.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on InN by Materials Project

InN is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. In3+ is bonded to four equivalent N3- atoms to form corner-sharing InN4 tetrahedra. There are three shorter (2.18 Å) and one longer (2.20 Å) In–N bond lengths. N3- is bonded to four equivalent In3+ atoms to form corner-sharing NIn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SmSe by Materials Project

SmSe is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Sm2+ is bonded to four equivalent Se2- atoms to form corner-sharing SmSe4 tetrahedra. All Sm–Se bond lengths are 2.84 Å. Se2- is bonded to four equivalent Sm2+ atoms to form corner-sharing SeSm4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbSe by Materials Project

TbSe is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Tb is bonded to four equivalent Se atoms to form corner-sharing TbSe4 tetrahedra. All Tb–Se bond lengths are 2.79 Å. Se is bonded to four equivalent Tb atoms to form corner-sharing SeTb4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdSe by Materials Project

CdSe is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent Se2- atoms to form corner-sharing CdSe4 tetrahedra. There are three shorter (2.69 Å) and one longer (2.70 Å) Cd–Se bond lengths. Se2- is bonded to four equivalent Cd2+ atoms to form corner-sharing SeCd4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdTe by Materials Project

CdTe is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent Te2- atoms to form corner-sharing CdTe4 tetrahedra. There are three shorter (2.87 Å) and one longer (2.88 Å) Cd–Te bond lengths. Te2- is bonded to four equivalent Cd2+ atoms to form corner-sharing TeCd4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CdO by Materials Project

CdO is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent O2- atoms to form corner-sharing CdO4 tetrahedra. There are three shorter (2.23 Å) and one longer (2.25 Å) Cd–O bond lengths. O2- is bonded to four equivalent Cd2+ atoms to form corner-sharing OCd4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrN by Materials Project

ZrN is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Zr3+ is bonded to four equivalent N3- atoms to form corner-sharing ZrN4 tetrahedra. There are one shorter (2.15 Å) and three longer (2.17 Å) Zr–N bond lengths. N3- is bonded to four equivalent Zr3+ atoms to form corner-sharing NZr4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlN by Materials Project

AlN is Wurtzite structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Al3+ is bonded to five equivalent N3- atoms to form a mixture of corner and edge-sharing AlN5 trigonal bipyramids. There are three shorter (1.91 Å) and two longer (2.09 Å) Al–N bond lengths. N3- is bonded to five equivalent Al3+ atoms to form a mixture of corner and edge-sharing NAl5 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CoO by Materials Project

CoO is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Co2+ is bonded to four equivalent O2- atoms to form corner-sharing CoO4 tetrahedra. There is one shorter (1.97 Å) and three longer (2.00 Å) Co–O bond length. O2- is bonded to four equivalent Co2+ atoms to form corner-sharing OCo4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZnO by Materials Project

ZnO is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Zn2+ is bonded to four equivalent O2- atoms to form corner-sharing ZnO4 tetrahedra. There are three shorter (2.00 Å) and one longer (2.01 Å) Zn–O bond lengths. O2- is bonded to four equivalent Zn2+ atoms to form corner-sharing OZn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent I1- atoms to form corner-sharing AgI4 tetrahedra. There are three shorter (2.87 Å) and one longer (2.89 Å) Ag–I bond lengths. I1- is bonded to four equivalent Ag1+ atoms to form corner-sharing IAg4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuH by Materials Project

CuH is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Cu1+ is bonded to four equivalent H1- atoms to form corner-sharing CuH4 tetrahedra. All Cu–H bond lengths are 1.73 Å. H1- is bonded to four equivalent Cu1+ atoms to form corner-sharing HCu4 tetrahedra.

36 MATERIALS SCIENCE↗