Formation and properties of rocksalt-type AlN and implications for high pressure phase relations in the system Si–Al–O–N

Schwarz, Marcus; Antlauf, Mathis; Schmerler, Steve; Keller, K.; Schlothauer, T.; Kortus, Jens; Heide, G.; Kroke, Edwin

doi:10.1080/08957959.2013.857020

Cited by 24 publications

(17 citation statements)

References 80 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is because the zero-temperature equilibrium volume is generally used in quasiharmonic calculations, and at high temperatures thermal expansion causes enough of a volume change to invalidate this approach. Our results agree with previous calculations using the QHA and with experimental data at temperatures below 2000 K [1,3,4,9,11,12,22]. In the lower panel of Fig.…”

Section: A Phase Stabilitysupporting

confidence: 83%

“…At room temperature, the transition has been experimentally shown to occur between 12 GPa [3] and 16 GPa [4]. Theoretical calculations at zero temperature recover this transition and have identified competing transition pathways from wurtzite to rocksalt: a uniaxial strain resulting in a tetragonal transition state, and a shear stress resulting in a hexagonal transition state [5][6][7], with the hexagonal pathway favored by AlN.…”

Section: Introductionmentioning

confidence: 92%

“…At temperatures below 1500 K anharmonic effects have negligible impact on Experimental data are collected from Refs. [1,3,4,11,22]. Theoretical data are extracted from Refs.…”

Section: A Phase Stabilitymentioning

confidence: 99%

See 2 more Smart Citations

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

et al. 2016

View full text Add to dashboard Cite

Wurtzite aluminium nitride (AlN) is a technologically important wide-band-gap semiconductor with an unusually high thermal conductivity, used in optical applications and as a heatsink substrate. Explaining many of its properties depends on an accurate description of its lattice dynamics, which have thus far only been captured in the quasiharmonic approximation. In this work, we show that anharmonic effects have a considerable impact on its phase stability and transport properties, since they are much stronger in the rocksalt phase. We construct a theoretical pressure-temperature phase diagram of AlN, demonstrating that the rocksalt phase is stabilized by increasing temperature, with respect to the wurtzite phase. We recover the thermal conductivity of the wurtzite phase (320 Wm −1 K −1 under ambient conditions) and compute the hitherto unknown thermal conductivity of the rocksalt phase (81 Wm −1 K −1 ). We also show that the electronic band gap decreases with temperature. These findings provide further evidence that anharmonic effects cannot be ignored in simulations of materials intended for high-temperature applications.

show abstract

Section: A Phase Stabilitysupporting

confidence: 83%

Section: Introductionmentioning

confidence: 92%

See 1 more Smart Citation

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Integrating over all possible states of the system is impossible, but the ergodic principle 59 states that as long as the system has no memory of its initial state, the ensemble average can be replaced by a time average: 17) which means that if the system is allowed to evolve with time it will eventually visit every possible state. Any molecular dynamics algorithm must satisfy the ergodicity principle to provide meaningful observables.…”

Section: Born-oppenheimer Molecular Dynamicsmentioning

confidence: 99%

“…It is also an optical semiconductor in its own right, emitting light at the ultraviolet end of the spectrum when doped with silicon. 16 Like other group III nitrides, AlN has been shown both experimentally and theoretically to undergo a pressure-induced phase transition from wurtzite to rocksalt at low temperatures, 17,18 although its high temperature behaviour is less clear due to the failure of the quasiharmonic approximation. 19,20,21,22,23 The rocksalt phase is metastable under ambient conditions, and can therefore only be synthesised in the form of thin films, for which it is difficult to measure the thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

Vibrations in solids : From first principles lattice dynamics to high temperature phase stability

Shulumba¹

2015

Linköping Studies in Science and Technology. Dissertations

View full text Add to dashboard Cite

In this thesis I introduce a new method for calculating the temperature dependent vibrational contribution to the free energy of a substitutionally disordered alloy that accounts for anharmonicity at high temperatures. This method exploits the underlying crystal symmetries in an alloy to make the calculations tractable. The validity of this approach is demonstrated by constructing the phase diagram via direct minimization of the Gibbs free energy of a notoriously awkward and technologically important system, Ti 1-x Al x N. The vibrational entropy including anharmonic effects is shown to be large and comparable to the configurational entropy at high temperatures, and with its inclusion, the theoretical miscibility gap of Ti 1-x Al x N is reduced from 6560 K to 2860 K, in line with atom probe experiments. A similar treatment of Zr 1-x Al x N and Hf 1-x Al x N alloys suggests that mass disorder has a minimal effect on phase stability compared with chemical ordering. My method is also capable of demonstrating that Hf 1-x Al x N, which is dynamically unstable at room temperature, is stabilised at high temperatures. Moreover I develop a new method of computing temperature dependent elastic constants for alloys from their phonon spectra, and show that for Ti 1-x Al x N, the elastic anisotropy is found to increase with temperature, helping to explain the spinodal decomposition.The effects of lattice dynamics on phase stability, mechanical, magnetic and transport properties on other materials are also examined. Four specific systems are discussed in detail. Firstly, in the case of CrN, lattice vibrations are shown to decrease the antiferromagnetic to paramagnetic phase transition temperature from 500 K to 380 K, in line with experimental evidence. Secondly, a temperature/pressure induced phase transition in AlN becomes much more facile than in the quasiharmonic approximation, and the thermal conductivity of the rocksalt phase is shown to be much lower than that of the wurtzite phase, as a result of the increased anharmonicity in the rocksalt structure. Thirdly, the temperature dependence of elastic constants of TiN becomes more isotropic as the temperature increases. Finally, iron carbides are evaluated as potentially important phases at the Earth's core; specifically, calculating the Gibbs free energy of a recently discovered orthorhombic phase of Fe 7 C 3 demonstrates that it is not stable relative to the known hexagonal phase at extreme pressure and temperatures.V Popular science summary Solid materials can be described using a simple mathematical model from the theory of lattice dynamics. In a solid, atoms are arranged in a regular and repeating structure (a lattice), and the forces between them can essentially be modelled as springs. Despite the simplicity of this model, it is possible to derive a surprising amount of information on materials from it. One can determine which arrangements of atoms, or phases, form the stable microscopic structures that we encounter in the real world, their mechanical properti...

show abstract

“114”‐Type Nitrides LnAl(Si_4−xAl_x)N₇O_δ with Unusual [AlN₆] Octahedral Coordination

Huang

Cao

et al. 2017

Angewandte Chemie

View full text Add to dashboard Cite

Aluminum–nitrogen six‐fold octahedral coordination, [AlN6], is unusual and has only been seen in the high‐pressure rocksalt‐type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si4−xAlx)N7Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6] coordination prepared via non‐high‐pressure synthesis. Structure refinements of neutron powder diffraction and single‐crystal X‐ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P63mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4] tetrahedra. Solid‐state NMR data of high‐purity La‐114 powders confirm the unusual [AlN6] coordination. These compounds are the first examples of the “33‐114” sub‐type in the “114” family. The additional site for over‐stoichiometric oxygen in the structure of 114‐type compounds was also identified.

show abstract

Formation and properties of rocksalt-type AlN and implications for high pressure phase relations in the system Si–Al–O–N

Cited by 24 publications

References 80 publications

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

Vibrations in solids : From first principles lattice dynamics to high temperature phase stability

“114”‐Type Nitrides LnAl(Si_4−xAl_x)N₇O_δ with Unusual [AlN₆] Octahedral Coordination

Contact Info

Product

Resources

About

Formation and properties of rocksalt-type AlN and implications for high pressure phase relations in the system Si–Al–O–N

Cited by 24 publications

References 80 publications

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN

Vibrations in solids : From first principles lattice dynamics to high temperature phase stability

“114”‐Type Nitrides LnAl(Si4−xAlx)N7Oδ with Unusual [AlN6] Octahedral Coordination

Contact Info

Product

Resources

About

“114”‐Type Nitrides LnAl(Si_4−xAl_x)N₇O_δ with Unusual [AlN₆] Octahedral Coordination