Abstract:In the present review, new approaches for the stabilization of metastable phases of zinc oxide and the growth of ZnO single crystals under high pressures and high temperatures are considered. The problems of the stabilization of the cubic modification of ZnO as well as solid solutions on its basis are discussed. A thermodynamic approach to the description of zinc oxide melting at high pressures is described which opens up new possibilities for the growth of both undoped and doped (for example, with elements of… Show more
“…However, it is clear that rs-Mg x Zn 1−x O alloys are composed of more than one phase with different optical properties, despite their apparent homogeneity according to the visual analysis of the XRD data. For example, a similar situation has recently been demonstrated for related rs-Ni x Zn 1−x O solid solutions which show distinct structural features in the ZnO-enriched region [38,39]. There, nonlinear behavior of thermal expansion coefficients is evident and may indicate that the solid solution in question is nonequilibrium.…”
The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgxZn1−xO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction. Transmission electron microscopy was used to study the particle size of nanocrystalline precursors, while the presence of Li, Na, and K metals in rock salt ZnO was detected by electron energy-loss spectroscopy and X-ray photoelectron spectroscopy in MgxZn1−xO alloys. Electron paramagnetic resonance measurements revealed the acceptor behavior of Li, Na, and K dopants based on the influence of the latter on native defects and natural impurities in ZnO-MgO alloys. In addition, diffuse reflectance spectroscopy was used to derive band gaps of quenched rock salt ZnO and its alloys with MgO.
“…However, it is clear that rs-Mg x Zn 1−x O alloys are composed of more than one phase with different optical properties, despite their apparent homogeneity according to the visual analysis of the XRD data. For example, a similar situation has recently been demonstrated for related rs-Ni x Zn 1−x O solid solutions which show distinct structural features in the ZnO-enriched region [38,39]. There, nonlinear behavior of thermal expansion coefficients is evident and may indicate that the solid solution in question is nonequilibrium.…”
The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgxZn1−xO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction. Transmission electron microscopy was used to study the particle size of nanocrystalline precursors, while the presence of Li, Na, and K metals in rock salt ZnO was detected by electron energy-loss spectroscopy and X-ray photoelectron spectroscopy in MgxZn1−xO alloys. Electron paramagnetic resonance measurements revealed the acceptor behavior of Li, Na, and K dopants based on the influence of the latter on native defects and natural impurities in ZnO-MgO alloys. In addition, diffuse reflectance spectroscopy was used to derive band gaps of quenched rock salt ZnO and its alloys with MgO.
“…These p – T conditions allowed us to ensure the completeness of the w-ZnO → rs-ZnO phase transition 13,16 and to avoid ZnO melting. 28 The synchrotron powder X-ray diffraction pattern (Fig. 3a) has shown that the recovered sample is single phase with no trace of w-ZnO.…”
Section: Resultsmentioning
confidence: 99%
“…No solid-state interaction was observed on the timescale of a few hours. 28 These results indicate that the stabilization of nanostructured rock-salt ZnO is not due to BN-ZnO interaction, which could influence the thermodynamics and kinetics (nucleation/growth) of the reverse transition to w-ZnO; but is mainly caused by mechanical aspects of compression/ decompression and sample environment. Also, we should not neglect the time-scale impact and the extreme sensitivity of phase transition s in ZnO to the p-T-t history of the w-ZnO precursor, 13 especially due to thermally induced deactivation of nucleation sites, already at temperatures of ∼400 K, and probably lower.…”
For complete and reproducible recovery of a high-pressure polymorph of zinc oxide, rock-salt ZnO (rs-ZnO), nanostructured wurtzite ZnO (w-ZnO) is typically used as a precursor for high-pressure synthesis. In the...
“…Among these structures, hexagonal würtzite (named HW–ZnO) is the most thermodynamically favoured and stable structure at normal ambient conditions. Nevertheless, the zinc blende (ZB) structure can be stabilized while growing on cubic substrates, and the cubic rocksalt (CRS) structure can be obtained at high pressure (over 9.5 GPa [ 8 , 38 ]). Fig.…”
Section: Properties and Synthesis Of Zno Nanowiresmentioning
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