99 research outputs found
Band structure of ZnO from resonant x-ray emission spectroscopy
Soft x-ray emission and absorption spectroscopy of the O K-edge are employed
to investigate the electronic structure of wurtzite ZnO(0001). A quasiparticle
band structure calculated within the GW approximation agrees well with the
data, most notably with the energetic location of the Zn3d - O2p hybridized
state and the anisotropy of the absorption spectra. Dispersion in the band
structure is mapped using the coherent k-selective part of the resonant x-ray
emission spectra. We show that a more extensive mapping of the bands is
possible in the case of crystalline anisotropy such as that found in ZnO.Comment: 5 pages, 5 figure
High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs
Tetragonal CuMnAs was the first antiferromagnet where reorientation of the
N\'eel vector was reported to occur by an inverse spin galvanic effect. A
complicating factor in the formation of phase-pure tetragonal CuMnAs is the
formation of an orthorhombic phase with nearly the same stoichiometry.
Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to
maintain a single phase in traditional solid state synthesis reactions. Here we
show that subtle differences in diffraction patterns signal pervasive
inhomogeneity and phase separation, even in Cu-rich CuMnAs.
From calorimetry and magnetometry measurements, we identify two transitions
corresponding to the N\'eel temperature (T) and an antiferromagnet to weak
ferromagnet transition in CuMnAs and
CuMnAs. These transitions have clear crystallographic
signatures, directly observable in the lattice parameters upon in-situ heating
and cooling. The immiscibility and phase separation could arise from a
spinoidal decomposition that occurs at high temperatures, and the presence of a
ferromagnetic transition near room temperature warrants further investigation
of its effect on the electrical switching behavior.Comment: 10 pages, 9 figures, added author middle initia
Solid-State Divalent Ion Conduction in ZnPS_3
Next-generation batteries based on divalent working ions have the potential to both reduce the cost of energy storage devices and increase performance. Examples of promising divalent systems include those based on Mg^(2+), Ca^(2+), and Zn^(2+) working ions. Development of such technologies is slow, however, in part due to the difficulty associated with divalent cation conduction in the solid state. Divalent ion conduction is especially challenging in insulating materials that would be useful as solid-state electrolytes or protecting layers on the surfaces of metal anodes. Furthermore, there are no reports of divalent cation conduction in insulating, inorganic materials at reasonable temperatures, prohibiting the development of structure–property relationships. Here, we report Zn^(2+) conduction in insulating ZnPS_3, demonstrating divalent ionic conductivity in an ordered, inorganic lattice near room temperature. Importantly, the activation energy associated with the bulk conductivity is low, 351 ± 99 meV, comparable to some Li+conductors such as LTTO, although not as low as the superionic Li+ conductors. First-principles calculations suggest that the barrier corresponds to vacancy-mediated diffusion. Assessment of the structural distortions observed along the ion diffusion pathways suggests that an increase in the P–P–S bond angle in the [P_2S_6]^(4–) moiety accommodates the Zn^(2+) as it passes through the high-energy intermediate coordination environments. ZnPS_3 now represents a baseline material family to begin developing the structure–property relationships that control divalent ion diffusion and conduction in insulating solid-state hosts
Solid-State Divalent Ion Conduction in ZnPS_3
Next-generation batteries based on divalent working ions have the potential to both reduce the cost of energy storage devices and increase performance. Examples of promising divalent systems include those based on Mg^(2+), Ca^(2+), and Zn^(2+) working ions. Development of such technologies is slow, however, in part due to the difficulty associated with divalent cation conduction in the solid state. Divalent ion conduction is especially challenging in insulating materials that would be useful as solid-state electrolytes or protecting layers on the surfaces of metal anodes. Furthermore, there are no reports of divalent cation conduction in insulating, inorganic materials at reasonable temperatures, prohibiting the development of structure–property relationships. Here, we report Zn^(2+) conduction in insulating ZnPS_3, demonstrating divalent ionic conductivity in an ordered, inorganic lattice near room temperature. Importantly, the activation energy associated with the bulk conductivity is low, 351 ± 99 meV, comparable to some Li+conductors such as LTTO, although not as low as the superionic Li+ conductors. First-principles calculations suggest that the barrier corresponds to vacancy-mediated diffusion. Assessment of the structural distortions observed along the ion diffusion pathways suggests that an increase in the P–P–S bond angle in the [P_2S_6]^(4–) moiety accommodates the Zn^(2+) as it passes through the high-energy intermediate coordination environments. ZnPS_3 now represents a baseline material family to begin developing the structure–property relationships that control divalent ion diffusion and conduction in insulating solid-state hosts
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