Anisotropic Phonon Scattering and Thermal Transport Property Induced by the Liquid-like Behavior of AgCrSe₂

Superionic conductors exhibiting a periodic crystalline lattice and liquid-like ionic conductivity have emerged as promising materials in energy-conversion devices. Herein, we have investigated the interplay among anharmonic lattice dynamics, thermal conduction, and ultrafast atomic diffusion across the superionic transition of AgCrSe2. We show that the thermal conductivity (κ) contributions from convection and conduction–convection interactions increase simultaneously due to the gradual fluidization of Ag atoms, leading to a temperature-independent κ in the superionic state. We demonstrate a non-Peierls type thermal transport behavior induced by the strong lattice anharmonicity of Ag atoms, which promotes a nontrivial wave-like phonon tunneling in the normal state of AgCrSe2. Our current fluctuation analysis demonstrates an anisotropic phonon-liquid scattering behavior that the in-plane nondispersive transverse acoustic (TA) phonons near the zone boundary collapse, while the zone center and boundary TA phonons in the direction perpendicular to the liquid-like flow of Ag atoms survive

Theoretical Study of Mononuclear Nickel(I), Nickel(0), Copper(I), and Cobalt(I) Dioxygen Complexes: New Insight into Differences and Similarities in Geometry and Bonding Nature

Geometries, bonding nature, and electronic structures of (N^∧N)­Ni­(O₂) (N^∧N = β-diketiminate), its cobalt­(I) and copper­(I) analogues, and (Ph₃P)₂Ni­(O₂) were investigated by density functional theory (DFT) and multistate restricted active space multiconfigurational second-order perturbation (MS-RASPT2) methods. Only (N^∧N)­Ni­(O₂) takes a <i>C</i>_S symmetry structure, because of the pseudo-Jahn–Teller effect, while all other complexes take a <i>C</i>_2V structure. The symmetry lowering in (N^∧N)­Ni­(O₂) is induced by the presence of the singly occupied δ_{d_<i>xy</i>–π_<i>x</i>^*} orbital. In all of these complexes, significant superoxo (O₂^–) character is found from the occupation numbers of natural orbitals and the O–O π* bond order, which is independent of the number of d electrons and the oxidation state of metal center. However, this is not a typical superoxo species, because the spin density is not found on the O₂ moiety, even in open-shell complexes, (N^∧N)­Ni­(O₂) and (N^∧N)­Co­(O₂). The M–O and O–O distances are considerably different from each other, despite the similar superoxo character. The M–O distance and the interaction energy between the metal and O₂ moieties are determined by the d_<i>yz</i> orbital energy of the metal moiety taking the valence state. The binding energy of the O₂ moiety is understood in terms of the d_<i>yz</i> orbital energy in the valence state and the promotion energy of the metal moiety from the ground state to the valence state. Because of the participations of various charge transfer (CT) interactions between the metal and O₂ moieties, neither the d_<i>yz</i> orbital energy nor the electron population of the O₂ moiety are clearly related to the O–O bond length. Here, the π bond order of the O₂ moiety is proposed as a good measure for discussing the O–O bond length. Because the d electron configuration is different among these complexes, the CT interactions are different, leading to the differences in the π bond order and, hence, the O–O distance among these complexes. The reactivity of dioxygen complex is discussed with the d_<i>yz</i> orbital energy

Mo–Mo Quintuple Bond is Highly Reactive in H–H, C–H, and O–H σ‑Bond Cleavages Because of the Polarized Electronic Structure in Transition State

The recently reported high reactivity of the Mo–Mo quintuple bond of Mo₂(N^∧N)₂ (<b>1</b>) {N^∧N = μ-κ²-CH­[N­(2,6-<i>i</i>Pr₂C₆H₃)]₂} in the H–H σ-bond cleavage was investigated. DFT calculations disclosed that the H–H σ-bond cleavage by <b>1</b> occurs with nearly no barrier to afford the <i>cis</i>-dihydride species followed by cis–trans isomerization to form the <i>trans</i>-dihydride product, which is consistent with the experimental result. The O–H and C–H bond cleavages by <b>1</b> were computationally predicted to occur with moderate (Δ<i>G</i>°^⧧ = 9.0 kcal/mol) and acceptable activation energies (Δ<i>G</i>°^⧧ = 22.5 kcal/mol), respectively, suggesting that the Mo–Mo quintuple bond can be applied to various σ-bond cleavages. In these σ-bond cleavage reactions, the charge-transfer (CT_Mo→XH) from the Mo–Mo quintuple bond to the X–H (X = H, C, or O) bond and that (CT_XH→Mo) from the X–H bond to the Mo–Mo bond play crucial roles. Though the HOMO (dδ-MO) of <b>1</b> is at lower energy and the LUMO + 2 (dδ*-MO) of <b>1</b> is at higher energy than those of RhCl­(PMe₃)₂ (LUMO and LUMO + 1 of <b>1</b> are not frontier MO), the H–H σ-bond cleavage by <b>1</b> more easily occurs than that by the Rh complex. Hence, the frontier MO energies are not the reason for the high reactivity of <b>1</b>. The high reactivity of <b>1</b> arises from the polarization of dδ-type MOs of the Mo–Mo quintuple bond in the transition state. Such a polarized electronic structure enhances the bonding overlap between the dδ-MO of the Mo–Mo bond and the σ*-antibonding MO of the X–H bond to facilitate the CT_Mo→XH and reduce the exchange repulsion between the Mo–Mo bond and the X–H bond. This polarized electronic structure of the transition state is similar to that of a frustrated Lewis pair. The easy polarization of the dδ-type MOs is one of the advantages of the metal–metal multiple bond, because such polarization is impossible in the mononuclear metal complex

Silicon As an Unexpected n‑Type Dopant in BiCuSeO Thermoelectrics

As a promising thermoelectric material, BiCuSeO is of great interest for energy conversion. A higher figure of merit in n-type BiCuSeO than that in the p-type was predicted from theory, suggesting a need of in-depth investigations on the doping effects. In this work, the influences of group IV elements (Si, Ge, Sn, and Pb) on the electronic structures of BiCuSeO are studied from first principles. Despite the similar electronegativities of the group IV elements, Si is found to be an n-type dopant, being distinctly different from Ge, Sn, and Pb, which exhibit typical p-type behaviors. Detailed analysis on the doping effects is performed based on a recently developed band unfolding technique. Furthermore, Si-doped BiCuSeO is shown to have a higher power factor than p-type BiCuSeO from the Boltzmann transport theory

Mo–Mo Quintuple Bond is Highly Reactive in H–H, C–H, and O–H σ‑Bond Cleavages Because of the Polarized Electronic Structure in Transition State

The recently reported high reactivity of the Mo–Mo quintuple bond of Mo₂(N^∧N)₂ (<b>1</b>) {N^∧N = μ-κ²-CH­[N­(2,6-<i>i</i>Pr₂C₆H₃)]₂} in the H–H σ-bond cleavage was investigated. DFT calculations disclosed that the H–H σ-bond cleavage by <b>1</b> occurs with nearly no barrier to afford the <i>cis</i>-dihydride species followed by cis–trans isomerization to form the <i>trans</i>-dihydride product, which is consistent with the experimental result. The O–H and C–H bond cleavages by <b>1</b> were computationally predicted to occur with moderate (Δ<i>G</i>°^⧧ = 9.0 kcal/mol) and acceptable activation energies (Δ<i>G</i>°^⧧ = 22.5 kcal/mol), respectively, suggesting that the Mo–Mo quintuple bond can be applied to various σ-bond cleavages. In these σ-bond cleavage reactions, the charge-transfer (CT_Mo→XH) from the Mo–Mo quintuple bond to the X–H (X = H, C, or O) bond and that (CT_XH→Mo) from the X–H bond to the Mo–Mo bond play crucial roles. Though the HOMO (dδ-MO) of <b>1</b> is at lower energy and the LUMO + 2 (dδ*-MO) of <b>1</b> is at higher energy than those of RhCl­(PMe₃)₂ (LUMO and LUMO + 1 of <b>1</b> are not frontier MO), the H–H σ-bond cleavage by <b>1</b> more easily occurs than that by the Rh complex. Hence, the frontier MO energies are not the reason for the high reactivity of <b>1</b>. The high reactivity of <b>1</b> arises from the polarization of dδ-type MOs of the Mo–Mo quintuple bond in the transition state. Such a polarized electronic structure enhances the bonding overlap between the dδ-MO of the Mo–Mo bond and the σ*-antibonding MO of the X–H bond to facilitate the CT_Mo→XH and reduce the exchange repulsion between the Mo–Mo bond and the X–H bond. This polarized electronic structure of the transition state is similar to that of a frustrated Lewis pair. The easy polarization of the dδ-type MOs is one of the advantages of the metal–metal multiple bond, because such polarization is impossible in the mononuclear metal complex

Unexpected High-Pressure Phase of GeTe with an Origin of Low Ionicity and Electron Delocalization

First-principles evolutionary searches have been performed to systematically explore the high-pressure phases of germanium telluride. Two new phases are found to be both energetically and dynamically stable under moderate pressures. A <i>Pnma</i> orthorhombic phase with an uncommon “boat” conformation and a <i>P</i>4/<i>nmm</i> tetragonal phase are found to become stable at ∼15 and ∼37 GPa, respectively. The long-believed high-pressure B2 phase, however, is found to be energetically unfavorable comparing to the <i>P</i>4/<i>nmm</i> phase. Our calculations of the electronic structures show that <i>Pnma</i>-boat GeTe and <i>P</i>4/<i>nmm</i> GeTe exhibit semimetallic and metallic behaviors, respectively. On the basis of the electron–phonon coupling calculations, <i>P</i>4/<i>nmm</i> GeTe is shown to have a superconducting transition at low temperatures, resulting from its sudden decrease of ionicity and the more delocalized lone-pair electrons. The discovery of these new GeTe phases further enriches our knowledge of the high-pressure behaviors of the IV–VI compounds

PERUBAHAN LUAS KAWASAN PANTAI DI PROVINSI BENGKULU BAGIAN SELATAN DENGAN MENGGUNAKAN DATA CITRA SATELIT LANDSAT PERIODE TAHUN 2006-2015

Perubahan luas kawasan pantai di Bengkulu bagian selatan yang mengalami abrasi dapat mengancam perumahan penduduk yang dekat dengan pantai, budidaya laut, dan tempat wisata serta sarana transportasi Jalinbar. Penelitian ini bertujuan untuk mengetahui luasan, kecepatan dan jenis perubahan luas kawasan pantai dengan teknologi penginderaan jauh. Metode penelitian ini menggunakan teknik overlay dari data Citra Satelit (Landasat-5 TM, Landsat-7 ETM + dan Landat-8 OLI) selama 10 tahun terakhir dari tahun 2006-2015. Hasil penelitian ini didapatkan rata-rata perubahan garis pantai di Bengkulu bagian Selatan yang mengalami abrasi terbesar terjadi di daerah Bengkulu Selatan dengan nilai 4,25 Ha/tahun serta rata-rata kecepatan abrasi mencapai 6,19-9,59 meter/tahun. Rata-rata perubahan garis pantai yang mengalami sedimentasi terjadi di daerah Kaur dengan nilai 7,94 Ha/tahun dan rata-rata kecepatan sedimentasi mencapai 10,62-18,74 meter/tahun. Secara umum, jenis perubahan garis pantai yang terjadi di wilayah Bengkulu bagian selatan mengalami sedimentasi yang diakibatkan oleh faktor alam dan faktor manusia. Kata kunci : Perubahan Luas Pantai, Abrasi, Sedimentasi, Citra Landsat, Bengkulu bagian selata

Comparison of effect of <i>mce3R</i> deletion on genes differentially expressed ≥1 log₂-fold in cholesterol in WT Mtb, after 4 hours exposure to cholesterol, pH 7 medium.

Comparison of effect of mce3R deletion on genes differentially expressed ≥1 log2-fold in cholesterol in WT Mtb, after 4 hours exposure to cholesterol, pH 7 medium.</p

Schematic illustration of Gaussian speed profiles of the random dot patterns (RDPs) used for speed discrimination.

<p>Each panel corresponds to a pair of RDPs with Gaussian speed distribution of a specific bandwidth, i.e. a specific level of speed noise. The x axis represents the range of speed. The y axis represents relative distributions across speed (The values are arbitrary). Corresponding to no noise, 0 SD means that a single speed is used for all dots in an RDP. Corresponding to low, medium and high level noise, 1, 2 and 4 SD mean that the movement of each dot in an RDP was independently drawn from a Gaussian distribution of speed, with the bandwidths 2, 4, and 8 degrees/sec. For a certain speed difference (or Weber speed ratio), the wider the Gaussian distribution, the more difficult speed discrimination is.</p

Comparison of effect of <i>mce3R</i> deletion on genes differentially expressed ≥1 log₂-fold in cholesterol, pH 5.7 in WT Mtb, after 4 hours exposure to cholesterol, pH 5.7 medium.

Comparison of effect of mce3R deletion on genes differentially expressed ≥1 log2-fold in cholesterol, pH 5.7 in WT Mtb, after 4 hours exposure to cholesterol, pH 5.7 medium.</p