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Title: Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure

Authors:
ORCiD logo; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Science Foundation (NSF)
OSTI Identifier:
1419069
Resource Type:
Journal Article
Resource Relation:
Journal Name: Crystals; Journal Volume: 8; Journal Issue: 2
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

James, Alwin, Esfahani, M., Woerner, William, Sinclair, Alexandra, Ehm, Lars, Oganov, Artem, and Parise, John. Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure. United States: N. p., 2018. Web. doi:10.3390/cryst8020015.
James, Alwin, Esfahani, M., Woerner, William, Sinclair, Alexandra, Ehm, Lars, Oganov, Artem, & Parise, John. Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure. United States. doi:10.3390/cryst8020015.
James, Alwin, Esfahani, M., Woerner, William, Sinclair, Alexandra, Ehm, Lars, Oganov, Artem, and Parise, John. 2018. "Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure". United States. doi:10.3390/cryst8020015.
@article{osti_1419069,
title = {Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure},
author = {James, Alwin and Esfahani, M. and Woerner, William and Sinclair, Alexandra and Ehm, Lars and Oganov, Artem and Parise, John},
abstractNote = {},
doi = {10.3390/cryst8020015},
journal = {Crystals},
number = 2,
volume = 8,
place = {United States},
year = 2018,
month = 1
}
  • The application of pressure in solid-state synthesis provides a route for the creation of new and exciting materials. However, the onerous nature of high-pressure techniques limits their utility in materials discovery. The systematic search for novel oxynitrides—semiconductors for photocatalytic overall water splitting—is a representative case where quench high-pressure synthesis is useful and necessary in order to obtain target compounds. We utilize state of the art crystal structure prediction theory (USPEX) and in situ synchrotron-based X-ray scattering to speed up the discovery and optimization of novel compounds using high-pressure synthesis. Using this approach, two novel oxynitride phases were discovered in themore » GaN–Nb2O5 system. The (Nb2O5)0.84:(NbO2)0.32:(GaN)0.82 rutile structured phase was formed at 1 GPa and 900 °C and gradually transformed to a α-PbO2-related structure above 2.8 GPa and 1000 °C. The low-pressure rutile type phase was found to have a direct optical band gap of 0.84 eV and an indirect gap of 0.51 eV.« less
  • The application of pressure in solid-state synthesis provides a route for the creation of new and exciting materials. However, the onerous nature of high-pressure techniques limits their utility in materials discovery. The systematic search for novel oxynitrides—semiconductors for photocatalytic overall water splitting—is a representative case where quench high-pressure synthesis is useful and necessary in order to obtain target compounds. In this paper, we utilize state of the art crystal structure prediction theory (USPEX) and in situ synchrotron-based X-ray scattering to speed up the discovery and optimization of novel compounds using high-pressure synthesis. Using this approach, two novel oxynitride phases weremore » discovered in the GaN–Nb 2O 5 system. The (Nb 2O 5) 0.84:(NbO 2) 0.32:(GaN) 0.82 rutile structured phase was formed at 1 GPa and 900°C and gradually transformed to a α-PbO 2-related structure above 2.8 GPa and 1000°C. The low-pressure rutile type phase was found to have a direct optical band gap of 0.84 eV and an indirect gap of 0.51 eV.« less
  • This paper reports on the voltage breakdown behavior of a plane-parallel gap of 0.48-mm length filled with helium that was examined at atmospheric pressure with admixtures of dry air at relative pressures of 0, 10{sup {minus}4}, 3 {times} 10{sup {minus}4}, and 10{sup {minus}3}. The initial stages of the breakdown were investigated by means of a quantitative model consisting of the electron, ion, and excited-particle conservation equations and the Poisson equation. The system of equations was solved for an applied voltage of 180 V, corresponding to a field of 3750 V cm{sup {minus}1}, at one single partial pressure of the impurities,more » pr = 10{sup {minus}4}. Two numerical routines were used for the solution: A commercial IMSL subroutine TWODEPEP, and a newly developed method of solution in several fractional steps. The results were compared up to about 15 {mu}s, at which time the growing instability of the commercial subroutine began to require an excessively long computer time: At this time, the ratio of the total numbers of electrons and ions obtained by the first and second method was 0.8 and 0.9, respectively. The axial profiles of the density of electrons, ions, and excited particles were obtained up to a time of 16.75 {mu}s, reaching maximum values of 6.8 {times} 10{sup 10} cm{sup {minus}3}, 4.9 {times} 10{sup 11} cm{sup {minus}3}, and 4.3 {times} 10{sup 12} cm{sup {minus}3}, respectively. The maximum value of the space-charge field attained at the cathode was 10.2 kV cm{sup {minus}1}. The experimental setup was designed to measure the initial rise of the breakdown current. Several series of measurements were performed at various overvoltages at each of the given impurity partial pressures.« less
  • Diamond anvil cell (DAC) based resistance measurements are carried out in AuAl{sub 2} to the pressures of about 25 GPa for the first time. The data indicate possibility of phase transition around 12 GPa. High pressure data obtained using Elettra synchrotron source confirm the transformation of AuAl{sub 2} from ambient CaF{sub 2} to orthorhombic phase. The high precision P-V data when transformed to universal equation of state does not show any deviation from linearity. The first principles electronic band structure calculations up to these pressures in the cubic phase do not reveal any change corroborating the experimental findings of nonobservationmore » of electronic topological transition in this compound.« less