arXiv subjects

Chunying Pu

Publications and source records attributed to Chunying Pu.

4 recordsLinked to original sources

arXiv2024

Novel properties of two-dimensional Janus transition metal hydrosulfides: electride states, charge density waves and superconductivity

Inspired by recent experimental synthesis of the two-dimensional Janus material MoSH, we have performed extensive first-principles calculations to investigate the characteristics of all possible Janus two-dimensional transition metal hydrosulfides (JTMSHs), in both the 2H and 1T phases. Our investigations revealed that the JTMSHs can form a unique family of two-dimensional materials with intriguing physical and chemical properties. In details, we have found that JTMSHs can exist in various states, exhibiting metallic, semiconducting, and magnetic character. One particularly intriguing finding considered identification of electride states with distinct bonding characteristics in the 2H-JTMSHs for TM=V, Nb, Ta, Mo, W and Tc. Additionally, we have observed evidence of charge density wave scenario in 1T-JTMSH with TM=Tc, Re, and W and 2H-JTMSH with TM = Tc. Importantly, by applying compressive strain to these materials, the charge density wave can be completely suppressed, eventually leading to the superconducting phase. In particular, we have shown that when subjected to a compressive strain within 10%, the superconducting transition temperature (TC) of 1T-WSH, 1T-TcSH and 2H-TcSH can reach values of 13.8, 16.2 and 24.2 K respectively. Moreover, our investigation also unveiled two intrinsic phonon-mediated superconductors, namely 2H-WSH and 1T-RuSH with TC of 17.0 and 8 K, respectively.

cond-mat.mtrl-sci↗

arXiv2018

Unexpected Xe cations and superconductivity in Y-Xe compounds under pressure

The metal-based noble gas compounds exhibit interesting behavior of electronic valence states under pressure. For example, Xe upon compression can gain electrons from the alkali metal, or lose electrons unexpectedly to Fe and Ni, toward formation of stable metal compounds. In addition, the Na2He is not even stabilized by the local chemical bonds but via the long-range Coulomb interactions. Herein, by using the first-principles calculations and the unbiased structure searching techniques, we uncover that the transition metal Y is able to react with Xe above 60 GPa within various Y-Xe stochiometries, namely the YXe, YXe2, YXe3 and Y3Xe structures. Surprisingly, it is found that all the resulting compounds are intermetallic and Xe atoms are positively charged. We also argue that the pressure-induced changes of the energy orbital filling are responsible for the electron transfer from Xe to Y. Meanwhile, the Peierls-like mechanism is found to stabilize the energetically most favorable YXe-Pbam phase. Furthermore, the predicted YXe-Pbam, YXe-Pnnm, and YXe3-I4/mcm phases are discovered to be phonon-mediated superconductors under pressure, with the critical superconducting temperatures in the range of approximately 3-4K, 7-10K, and 5-6K, respectively. In summary, our work promotes further understanding of the crystal structures and electronic properties of the metal-based noble gas compounds.

cond-mat.mtrl-sci↗

arXiv2018

Prediction of Stable Ground-State Uranium Nitrides at Ambient and High Pressures

Uranium nitrides have been the subject of intense research owing to their potential applications as advanced nuclear fuels. However, the phase diagram of the U-N system at low temperature and high pressure still remains unclear. In this paper, we explore extensively the phase diagram of the U-N system up to 150 GPa based on first-principles swarm structure searches. The phase diagrams of the experimentally known stoichiometries like U2N3 and UN2 are refined. At zero temperature and pressure, the experimentally observed CaF2-type UN2 is found to transform into another new I41/amd-type UN2, which is related to the dynamical instability originated from Peierls mechanism. Two new stable high-pressure phases of U2N3 and UN2 are identified for the first time. Besides, several new chemical stoichiometries (UN4, UN3, U3N5 and U2N) are found to have stability fields on the U-N phase diagram. The pressure-induced phase transitions for the U-N system are further investigated. The peculiar structural features such as N2-dimers, planar SO3-like N(N)3 units, non-coplarnar zigzag N4 units, and zigzag U chains are found in U-N compounds under pressure. Our results on the structure exploring provide a better understanding of the structural characteristics and physical properties of uranium nitrides under pressure.

physics.comp-ph↗

arXiv2017

Pressure-induced metallization and superconducting phase in ReS2

Among the family of TMDs, ReS2 takes a special position, which crystalizes in a unique distorted low-symmetry structure at ambient conditions. The interlayer interaction in ReS2 is rather weak, thus its bulk properties are similar to that of monolayer. However, how does compression change its structure and electronic properties is unknown so far. Here using ab initio crystal structure searching techniques, we explore the high-pressure phase transitions of ReS2 extensively and predict two new high-pressure phases. The ambient pressure phase transforms to a "distorted-1T" structure at very low pressure and then to a tetragonal I41/amd structure at around 90 GPa. The "distorted-1T" structure undergoes a semiconductor-metal transition (SMT) at around 70 GPa with a band overlap mechanism. Electron-phonon calculations suggest that the I41/amd structure is superconducting and has a critical superconducting temperature of about 2 K at 100 GPa. We further perform high-pressure electrical resistance measurements up to 102 GPa. Our experiments confirm the SMT and the superconducting phase transition of ReS2 under high pressure. These experimental results are in good agreement with our theoretical predictions.

cond-mat.mtrl-sci↗