Narrow Results

Analysis of cultural heritage samples by PIXE involves the risk of damaging precious samples due to MeV-proton irradiation. To investigate appropriate methods to detect invisible damage due to PIXE analysis, we analyzed the change in chemical bonding of the sample surface subjected to PIXE and RBS measurement by Fourier Transform InfraRed spectroscopy (FT-IR). We used Japanese hemp paper as a simulated cultural property sample. The proton irradiation for the PIXE/RBS measurement was performed in a vacuum with an incident beam energy of 2.5 MeV, a beam current of 1 nA, and an irradiation time up to 10 min. The corresponding beam flux and fluence were 0.06 nA/mm² and 4 $\mu$Coulomb/cm², respectively. When the irradiation time was 10 min, the absorbed dose was 480 kGy on the sample surface. We identified neither change of elemental composition nor visible change such as discoloration due to irradiation. However, we found changes in peak heights in the measured FT-IR spectra, which suggest the destruction of chemical bonds such as O–H and C–O due to proton-induced radiation damage.

Structural, elastic, electronic and optical properties as well as chemical bonding of the binary alkali metal selenides M₂ Se (M = Li, Na, K, Rb) were calculated using the full potential linearized augmented plane method. From the elastic constants it is inferred that these compounds are brittle in nature. The results of the electronic band structure show that Na₂Se has a direct energy band gap (Γ-Γ), Li₂Se has an indirect energy band gap (Γ- X), while K₂Se and Rb₂Se have an indirect energy band gap (X-Γ). Analysis of the charge distribution plots reveals a dominated ionic bonding in the herein studied compounds. Additionally, we have calculated the optical properties, namely, the real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, optical conductivity and reflectivity for radiation up to 30.0 eV. All these compounds have direct energy band gap greater than 3.1 eV suggesting their use for manufacturing high frequency devices.

Using first-principles calculation we investigated the structural, electronic and elastic properties of paramagnetic CaFeAs₂. Our results indicated that the density of states (DOS) was dominated predominantly by Fe-3$d$ states at Fermi levels, and stronger hybridization exists between As₁ and As₁ atoms. Three hole pockets are formed at $\mathrm{\Gamma }$ and Z points, and two electronic pockets are formed at A and E points. The Dirac cone-like bands appear near B and D points. For the first time we calculated the elastic properties and found that CaFeAs₂ is a mechanically stable and moderately hard material, it has elastic anisotropy and brittleness, which agrees well with the bonding picture and the calculation of Debye temperature (${\mathrm{\Theta }}_{\mathrm{\text{D}}}$).

Perovskites CaPd₃B₄O${}_{12}$ (B = Ti, V) are studied theoretically using generalized gradient approximation (GGA), GGA-modified Becke–Johnson (GGA-mBJ), GGA with spin-orbit coupling (GGA + SOC) and hybrid functional (HF) in the domain of density functional theory (DFT). The estimated structural parameters are reliable with the experimentally reported data. Cohesive energy and enthalpy show that these compounds are stable thermodynamically. Bonding nature makes known that the chemical bond between Ca/Ti–O is ionic, Pd/V–O is covalent and Ti/V–Ti/V is metallic. The mechanical properties show that these compounds are stable, elastically anisotropic and ductile in nature. CaPd₃Ti₄O${}_{12}$ is a 2.94 eV direct-wide bandgap semiconductor through GGA-mBJ and consistent with experiments. The optical properties show that CaPd₃Ti₄O${}_{12}$ is a good dielectric material. The dense electronic states and the wide-gap semiconductor nature of CaPd₃Ti₄O${}_{12}$ suggest that it can be used as a good thermoelectric material.

The electronic structure of AgCd₂GaS₄ crystal has been studied with X-ray photoelectron spectroscopy (XPS). Chemical bonding effects have been observed by comparative analysis of binding energies of element core levels and crystal structure of AgCd₂GaS₄ and several ternary sulfides. It has been shown for Ga-bearing sulfides that the increase of mean chemical bond length between gallium and sulfur ions is directly related to the decrease of chemical shift of cation core level binding energy.

Wide set of experimental results on binding energy of photoelectrons emitted from P 2p, P 2s, and O 1s core levels has been observed for inorganic phosphate crystals and the parameters were compared using energy differences Δ(O 1s - P 2p) and Δ (O 1s - P 2s) as most robust characteristics. Linear dependence of the binding energy difference on mean chemical bond length L(P–O) between phosphorus and oxygen atoms has been found. The functions are of the forms: Δ (O 1s - P 2p) (eV) = 375.54 + 0.146 · L(P–O) (pm) and Δ (O 1s - P 2s) (eV) = 320.77 + 0.129 · L(P–O) (pm). The dependencies are general for inorganic phosphates and may be used in quantitative component analysis of X-ray photoemission spectra of complex oxide compounds including functional groups with different coordination of P and O atoms.

Continuous development of liquid/solid interface towards the liquid side promotes crystal growth under the chemical reaction among crystal constituents. Here, factors that determine inorganic functional materials are analyzed by establishing the chemical reaction equations at liquid/solid interface. The linear growth velocity along the [uvw] direction is directly determined by the chemical bonds formed in chemical reaction at the growing interface. In the present chemical bonding growth model, both thermodynamic and kinetic controls are integrated, which can also be classified in particular materials growth system. Taking Cu₂O as an example, we demonstrate that the critical control factor is the bonding mode in linking Cu₂O growth units controlled by chemical reaction, and various bonding modes promote the polymorph growth of inorganic functional materials.

Electronic state of monovalent ions in superionic conductors α-AgI and Li₃N was calculated by the DV-Xα cluster method. The movements of the cations were simulated by several model clusters with different position of the moving cation. The net charge of moving cations and the total bond overlap population between the moving cation and the other ions were used for discussion of chemical bonding of the moving cation. In both superionic conductors, the total bond overlap population of the moving cation along the conduction path less changed than those of the other paths. On the other hand, the change of the net charge of the moving cation was similar in any paths. These results suggest that the smaller change of the total bond overlap population of the moving cations should play an important role in the fast ion conduction in superionic conductors, rather than the change of the net charge of the moving cation.