Physical-Mathematical modeling and numerical simulations of stress-strain state in seismic and volcanic regions

The strain-stress state generated by faulting or cracking and influenced by the strong heterogeneity of the internal earth structure precedes and accompanies volcanic and seismic activity. Particularly, volcanic eruptions are the culmination of long and complex geophysical processes and physical processes which involve the generation of magmas in the mantle or in the lower crust, its ascent to shallower levels, its storage and differentiation in shallow crustal chambers, and, finally, its eruption at the Earth’s surface. Instead, earthquakes are a frictional stick-slip instability arising along pre-existing faults within the brittle crust of the Earth. Long-term tectonic plate motion causes stress to accumulate around faults until the frictional strength of the fault is exceeded. The study of these processes has been traditionally carried out through different geological disciplines, such as petrology, structural geology, geochemistry or sedimentology. Nevertheless, during the last two decades, the development of physical of earth as well as the introduction of new powerful numerical techniques has progressively converted geophysics into a multidisciplinary science. Nowadays, scientists with very different background and expertises such as geologist, physicists, chemists, mathematicians and engineers work on geophysics. As any multidisciplinary field, it has been largely benefited from these collaborations. The different ways and procedures to face the study of volcanic and seismic phenomena do not exclude each other and should be regarded as complementary. Nowadays, numerical modeling in volcanology covers different pre-eruptive, eruptive and post-eruptive aspects of the general volcanic phenomena. Among these aspects, the pre-eruptive process, linked to the continuous monitoring, is of special interest because it contributes to evaluate the volcanic risk and it is crucial for hazard assessment, eruption prediction and risk mitigation at volcanic unrest. large faults. The knowledge of the actual activity state of these sites is not only an academic topic but it has crucial importance in terms of public security and eruption and earthquake forecast. However, numerical simulation of volcanic and seismic processes have been traditionally developed introducing several simplifications: homogeneous half-space, flat topography and elastic rheology. These simplified assumptions disregards effects caused by topography, presence of medium heterogeneity and anelastic rheology, while they could play an important role in Moreover, frictional sliding of a earthquake generates seismic waves that travel through the earth, causing major damage in places nearby to the modeling procedure This thesis presents mathematical modeling and numerical simulations of volcanic and seismic processes. The subject of major interest has been concerned on the developing of mathematical formulations to describe seismic and volcanic process. The interpretation of geophysical parameters requires numerical models and algorithms to define the optimal source parameters which justify observed variations. In this work we use the finite element method that allows the definition of real topography into the computational domain, medium heterogeneity inferred from seismic tomography study and the use of complex rheologies. Numerical forward method have been applied to obtain solutions of ground deformation expected during volcanic unrest and post-seismic phases, and an automated procedure for geodetic data inversion was proposed for evaluating slip distribution along surface rupture

Chemical Design and Example of Transparent Bipolar Semiconductors

Transparent bipolar semiconductors (TBSCs) are in demand for transparent electronics to serve as the basis for next generation optoelectronic devices. However, the poor carrier controllability in wide-bandgap materials makes the realization of a bipolar nature difficult. Only two materials, CuInO₂ and SnO, have been reported as TBSCs. To satisfy demand for the coexistence of transparency and bipolarity, we propose a design concept with three strategies; choice of early transition metals (eTM) such as Y³⁺ and Zr⁴⁺ for improving controllability of carrier doping, design of chemical bonds to obtain an appropriate band structure for bipolar doping, and use of a forbidden band-edge transition to retain transparency. This approach is verified through a practical examination of a candidate material, tetragonal ZrOS, which is chosen by following the criteria. ZrOS exhibits an excellent controllability of the electrical conductivity (10^–7–10^–2 S cm^–1), <i>p</i>- or <i>n</i>-type nature with ∼10^–2 S cm^–1 by Y or F doping, respectively, and optically wide gap (below 10^–4 cm^–1 up to ∼2.5 eV). This concept provides a new kind of TBSC based on eTM ionic compounds

SnAs with the NaCl-type Structure: Type‑I Superconductivity and Single Valence State of Sn

We examined the superconductivity of SnAs and the valence state of Sn in its lattice with an expectation that SnAs and related compounds with the NaCl-type structure might exhibit superconductivity at a high critical temperature (<i>T</i>_c), as (Ba_1–<i>x</i>K_<i>x</i>)­BiO₃ (BKBO) does, owing to the similar crystallographic and chemical environments of Sn in SnAs and Bi in BKBO. Although SnAs had low <i>T</i>_c, 3.58 K, we clarified two important characteristics: First, SnAs exhibits weakly coupled type-I superconductivity. Second, Sn has a single valence state, like Sn³⁺(5s¹), originating from there being only one crystallographically independent site in its NaCl-type structure. This unconventional single chemical state of Sn in SnAs would explain the superconductivity of SnAs with a three-dimensional NaCl-type structure, rather than a two-dimensional layered structure

<i>In Situ</i> Tuning of Magnetization and Magnetoresistance in Fe₃O₄ Thin Film Achieved with All-Solid-State Redox Device

An all-solid-state redox device composed of Fe₃O₄ thin film and Li⁺ ion conducting solid electrolyte was fabricated for use in tuning magnetization and magnetoresistance (MR), which are key factors in the creation of high-density magnetic storage devices. Electrical conductivity, magnetization, and MR were reversibly tuned by Li⁺ insertion and removal. Tuning of the various Fe₃O₄ thin film properties was achieved by donation of an electron to the Fe³⁺ ions. This technique should lead to the development of spintronics devices based on the reversible switching of magnetization and spin polarization (<i>P</i>). It should also improve the performance of conventional magnetic random access memory (MRAM) devices in which the ON/OFF ratio has been limited to a small value due to a decrease in <i>P</i> near the tunnel barrier

Water Durable Electride Y₅Si₃: Electronic Structure and Catalytic Activity for Ammonia Synthesis

We report an air and water stable electride Y₅Si₃ and its catalytic activity for direct ammonia synthesis. It crystallizes in the Mn₅Si₃-type structure and confines 0.79/f.u. anionic electrons in the quasi-one-dimensional holes. These anionic electrons strongly hybridize with yttrium 4d electrons, giving rise to improved chemical stability. The ammonia synthesis rate using Ru­(7.8 wt %)-loaded Y₅Si₃ was as high as 1.9 mmol/g/h under 0.1 MPa and at 400 °C with activation energy of ∼50 kJ/mol. Its strong electron-donating ability to Ru metal of Y₅Si₃ is considered to enhance nitrogen dissociation and reduce the activation energy of ammonia synthesis reaction. Catalytic activity was not suppressed even after Y₅Si₃, once dipped into water, was used as the catalyst promoter. These findings provide novel insights into the design of simple catalysts for ammonia synthesis

Mn Self-Doping of Orthorhombic RMnO₃ Perovskites: (R_0.667Mn_0.333)MnO₃ with R = Er–Lu

Orthorhombic rare-earth trivalent manganites RMnO₃ (R = Er–Lu) were self-doped with Mn to form (R_0.667Mn_0.333)­MnO₃ compositions, which were synthesized by a high-pressure, high-temperature method at 6 GPa and about 1670 K from R₂O₃ and Mn₂O₃. The average oxidation state of Mn is 3+ in (R_0.667Mn_0.333)­MnO₃. However, Mn enters the A site in the oxidation state of 2+, creating the average oxidation state of 3.333+ at the B site. The presence of Mn²⁺ was confirmed by hard X-ray photoelectron spectroscopy measurements. Crystal structures were studied by synchrotron powder X-ray diffraction. (R_0.667Mn_0.333)­MnO₃ crystallizes in space group <i>Pnma</i> with <i>a</i> = 5.50348(2) Å, <i>b</i> = 7.37564(1) Å, and <i>c</i> = 5.18686(1) Å for (Lu_0.667Mn_0.333)­MnO₃ at 293 K, and they are isostructural with the parent RMnO₃ manganites. Compared with RMnO₃, (R_0.667Mn_0.333)­MnO₃ exhibits enhanced Néel temperatures of about <i>T</i>_N1 = 106–110 K and ferrimagnetic or canted antiferromagnetic properties. Compounds with R = Er and Tm show additional magnetic transitions at about <i>T</i>_N2 = 9–16 K. (Tm_0.667Mn_0.333)­MnO₃ exhibits a magnetization reversal or negative magnetization effect with a compensation temperature of about 16 K

Valence Transitions in Negative Thermal Expansion Material SrCu₃Fe₄O₁₂

The valence states of a negative thermal expansion material, SrCu₃Fe₄O₁₂, are investigated by X-ray absorption and ⁵⁷Fe Mössbauer spectroscopy. Spectroscopic analyses reveal that the appropriate ionic model of this compound at room temperature is Sr²⁺Cu^∼2.4+₃Fe^∼3.7+₄O₁₂. The valence states continuously transform to Sr²⁺Cu^∼2.8+₃Fe^∼3.4+₄O₁₂ upon cooling to ∼200 K, followed by a charge disproportionation transition into the Sr²⁺Cu^∼2.8+₃Fe³⁺_∼3.2Fe⁵⁺_∼0.8O₁₂ valence state at ∼4 K. These observations have established the charge-transfer mechanism in this compound, and the electronic phase transitions in SrCu₃Fe₄O₁₂ can be distinguished from the first-order charge-transfer phase transitions (3Cu²⁺ + 4Fe^3.75+ → 3Cu³⁺ + 4Fe³⁺) in Ln³⁺Cu²⁺₃Fe^3.75+₄O₁₂ (Ln = trivalent lanthanide ions)

Narrow Bandgap in β‑BaZn₂As₂ and Its Chemical Origins

β-BaZn₂As₂ is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that β-BaZn₂As₂ and LaZnAsO have similar bandgaps; however, the bandgap of β-BaZn₂As₂ (previously reported value ∼0.2 eV) is 1 order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of β-BaZn₂As₂ is determined to be 0.23 eV from the intrinsic region of the temperature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemical bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct As–As hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the nonbonding Ba 5d_<i>x</i>²_{–<i>y</i>²} orbitals form an unexpectedly deep conduction band minimum (CBM) in β-BaZn₂As₂ although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between β-BaZn₂As₂ and LaZnAsO

Stimulation of Electro-oxidation Catalysis by Bulk-Structural Transformation in Intermetallic ZrPt₃ Nanoparticles

Although compositional tuning of metal nanoparticles (NPs) has been extensively investigated, possible control of the catalytic performance through bulk-structure tuning is surprisingly overlooked. Here we report that the bulk structure of intermetallic ZrPt₃ NPs can be engineered by controlled annealing and their catalytic performance is significantly enhanced as the result of bulk-structural transformation. Chemical reduction of organometallic precursors yielded the desired ZrPt₃ NPs with a cubic FCC-type structure (<i>c</i>-ZrPt₃ NPs). The <i>c</i>-ZrPt₃ NPs were then transformed to a different phase of ZrPt₃ with a hexagonal structure (<i>h</i>-ZrPt₃ NPs) by annealing at temperatures between 900 and 1000 °C. The <i>h</i>-ZrPt₃ NPs exhibited higher catalytic activity and long-term stability than either the <i>c</i>-ZrPt₃ NPs or commercial Pt/C NPs toward the electro-oxidation of ethanol. Theoretical calculations have elucidated that the enhanced activity of the <i>h</i>-ZrPt₃ NPs is attributed to the increased surface energy, whereas the stability of the catalyst is retained by the lowered bulk-free-energy

Glassy Distribution of Bi³⁺/Bi⁵⁺ in Bi_1–<i>x</i>Pb_<i>x</i>NiO₃ and Negative Thermal Expansion Induced by Intermetallic Charge Transfer

The valence distribution and local structure of Bi_1–<i>x</i>Pb_<i>x</i>NiO₃ (<i>x</i> ≤ 0.25) were investigated by comprehensive studies of Rietveld analysis of synchrotron X-ray diffraction (SXRD) data, X-ray absorption spectroscopy (XAS), hard X-ray photoemission spectroscopy (HAXPES), and pair distribution function (PDF) analysis of synchrotron X-ray total scattering data. Disproportionation of Bi ions into Bi³⁺ and Bi⁵⁺ was observed for all the samples, but it was a long-ranged one with distinct crystallographic sites in the <i>P</i>1̅ triclinic structure for <i>x</i> ≤ 0.15, while the ordering was short-ranged for <i>x</i> = 0.20 and 0.25. An intermetallic charge transfer between Bi⁵⁺ and Ni²⁺, leading to large volume shrinkage, was observed for all the samples upon heating at ∼500 K