authoren Lithium/potassium borohydride LiK(BH4)2 was recently synthesized and reported to be in a Pnma phase at ambient conditions. Subsequent theoretical studies show that this phase is metastable at finite temperatures up to 400 K. Studying the Pnma phase of LiK(BH4)2 by first‐principles calculations, we show that this phase is dynamically stable. Although the Pnma phase is metastable at finite temperatures as reported by previous studies, we find that it can be significantly stabilized by compression. Based on the structural similarity between the reactant LiBH4 and the product LiK(BH4)2 of the synthesization reaction, we suggest that the formation of the Pnma phase of LiK(BH4)2 may be driven by the kinetic of the reaction, according to the empirical Ostwald's steps rule in crystal nucleation. Therefore, it may be interesting to explore other possible low‐energy phases of LiK(BH4)2 by recently developed structure prediction methods.
We present a theory of the low-temperature mobility of electrons in a Gaussian heavily doped zinc oxide surface quantum well ͑ZnO SFQW͒, taking into account both surface impurity and surface roughness scattering. The theory also includes strong confinement due to spontaneous polarization charges on the surface of ZnO. The electron distribution is found to be shifted closer to the surface for the O-polar face, while far away therefrom for the Zn-polar one. Accordingly, both scatterings are remarkably enhanced in the former case, while reduced in the latter one. Further, high-temperature Coulomb correlation among the charged impurities at a high density in a sample subjected to thermal treatment is proven to significantly reduce scattering by them. Therefore, in such a sample, surface roughness scattering dominates the electron mobility, while for a sample without thermal treatment, both scatterings are important. Our theory provides a good quantitative explanation of the experimental data on electron transport, in particular, the different carrier-density dependences of the mobilities measured in O-polar face ZnO SFQWs prepared in different ways, by bombardment with H 2 + ions and by exposure to He + ions, which has not been explained so far.
Debye temperature and Frenkel temperature of liquid water at atmospheric pressure are estimated from the modified phonon-polariton model. Moreover, the decrease in the Debye temperature and the increase in the Frenkel temperature as rising temperature are pointed out. The heat capacity of liquid water is given by the phonon theory reported in 2012, covering both classical to quantum regimes for both the motion of phonon polariton and the di˙usion motion of particles. Because the ratio between temperature and the Debye temperature varies from 0.8 to 1.5, leading to the temperature independence of the heat capacity of liquid water at atmospheric pressure, in agreement with experimental work.
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