The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism

Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.

Electrochemical investigation of the P2–NaxCoO2 phase diagram.

Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.

Electronic structure of the high-temperature oxide superconductors

Thermoelectric effects enable direct conversion between thermal and electrical energy and provide an alternative route for power generation and refrigeration. Over the past ten years, the exploration of high-performance thermoelectric materials has attracted great attention from both an academic research perspective and with a view to industrial applications. This review summarizes the progress that has been made in recent years in developing thermoelectric materials with a high dimensionless figure of merits (ZT) and the related fabrication processes for producing nanostuctured materials. The challenge to develop thermoelectric materials with superior performance is to tailor the interconnected thermoelectric physical parameters — electrical conductivity, Seebeck coefficient and thermal conductivity — for a crystalline system. Nanostructures provide a chance to disconnect the linkage between thermal and electrical transport by introducing some new scattering mechanisms. Recent improvements in thermoelectric efficiency appear to be dominated by efforts to reduce the lattice thermal conductivity through nanostructural design. The materials focused in this review include Bi–Te alloys, skutterudite compounds, Ag–Pb–Sb–Te quaternary systems, half-Heusler compounds and some high-ZT oxides. Possible future strategies for developing thermoelectric materials are also discussed.

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High-performance nanostructured thermoelectric materials

Porosity plays a clearly important role in geology. It controls fluid storage in aquifers, oil and gas fields and geothermal systems, and the extent and connectivity of the pore structure control fluid flow and transport through geological formations, as well as the relationship between the properties of individual minerals and the bulk properties of the rock. In order to quantify the relationships between porosity, storage, transport and rock properties, however, the pore structure must be measured and quantitatively described. The overall importance of porosity, at least with respect to the use of rocks as building stone was recognized by TS Hunt in his “Chemical and Geological Essays” (1875, reviewed by JD Dana 1875) who noted:

> “Other things being equal, it may properly be said that the value of a stone for building purposes is inversely as its porosity or absorbing power.”

In a Geological Survey report prepared for the U.S. Atomic Energy Commission, Manger (1963) summarized porosity and bulk density measurements for sedimentary rocks. He tabulated more than 900 items of porosity and bulk density data for sedimentary rocks with up to 2,109 porosity determinations per item. Amongst these he summarized several early studies, including those of Schwarz (1870–1871), Cook (1878), Wheeler (1896), Buckley (1898), Gary (1898), Moore (1904), Fuller (1906), Sorby (1908), Hirschwald (1912), Grubenmann et al. (1915), and Kessler (1919), many of which were concerned with rocks and clays of commercial utility. There have, of course, been many more such determinations since that time.

There are a large number of methods for quantifying porosity, and an increasingly complex idea of what it means to do so. Manger (1963) listed the techniques by which the porosity determinations he summarized were made. He separated these into seven methods for …

/pdf/characterization-and-analysis-of-porosity-and-pore-sea0mqjsa8.pdf

Characterization and Analysis of Porosity and Pore Structures

We describe a multipurpose neutron powder diffractometer for high-efficiency and high-resolution measurements, HERMES, which has been installed at the JRR-3M reactor in Japan Atomic Energy Research Institute. To obtain high-quality data for a short counting time, or with a small sample amount, HERMES has a multi-detector system which consists of 150 3He neutron detectors and simple window type collimation. The best resolution is Δ2θ of 18' and Δd/d of 3 ×10-3, where 2θ and d are scattering-angle and d-spacing, respectively. The duration of an ordinary powder diffraction experiment is 1–5 h under the present conditions in JRR-3M. Some typical results of powder diffraction experiments and performance are given in this paper. We also show a result of 2D intensity mapping of magnetic diffuse scattering from a single crystal of a spin glass material.

https://iopscience.iop.org/article/10.1143/JJAP.37.3319/pdf

The new neutron powder diffractometer with a multi-detector system for high-efficiency and high-resolution measurements

Electric resistivity, thermoelectric power and thermal conductivity of a polycrystalline sample of the composite crystal [Ca2CoO3.34]0.614[CoO2], also known as Ca3Co4O9, have been measured below 300 K. Metallic conductivity accompanied by large thermoelectric power has been observed down to 50 K. At 300 K, the sample exhibits a thermoelectric power of S = 133 µVK-1, resistivity of ρ= 15 mΩcm and thermal conductivity of κ= 9.8 mWK-1cm-1. The resulting dimensionless figure of merit becomes ZT300 = 3.5×10-2, which is comparable to the value reported for a polycrystalline sample of NaCo2O4, indicating that the title compound is a potential candidate for a thermoelectric material.

https://iopscience.iop.org/article/10.1143/JJAP.39.L531/pdf

Low-Temperature Thermoelectric Properties of the Composite Crystal [Ca 2CoO 3.34] 0.614[CoO 2]

We have determined the crystal structure of the composite crystal [Ca 2 CoO 3 ] 0.62 CoO 2 , known as Ca 3 Co 4 O 9 , by a superspace group approach. Structural parameters were refined with a super...

Modulated Structure of the Thermoelectric Compound [Ca2CoO3]0.62CoO2

Preparation of Bi2Te3 films by electrodeposition

The crystal structure of a polycrystalline sample of higher manganese silicide (HMS) has been determined by means of the $(3+1)$-dimensional superspace group approach. The structural parameters were refined with a superspace group of $I{4}_{1}/amd(00\ensuremath{\gamma})00ss$ using powder neutron-diffraction data collected at 295 K. The compound belongs to a composite crystal family consisting of [Mn] and [Si] subsystems, with an irrational $c$-axis ratio (misfit parameter) of $\ensuremath{\gamma}={c}_{\text{Mn}}/{c}_{\text{Si}}\ensuremath{\sim}1.74$. Significant in-plane rotational modulation was revealed in the ``chimney''-[Si] subsystem, while positional modulation in the ``ladder''-[Mn] subsystem was only realized along ${c}_{\text{Mn}}$. The electronic structure of the sample was calculated on the basis of a commensurate approximation of the modulated structure using the full potential linearized augmented plane-wave method. The obtained band gap of ${E}_{g}\ensuremath{\sim}0.6\text{ }\text{eV}$ agreed well with the experimentally observed one. It appears that the band gap and density of states of the HMS samples depend on the positional modulation of the Si atoms. The various controversial formulas (for example, ${\text{Mn}}_{4}{\text{Si}}_{7}$, ${\text{Mn}}_{11}{\text{Si}}_{19}$, and so on) of the HMS phases reported thus far can be regarded as commensurate cases of a series of incommensurate ${\text{MnSi}}_{\ensuremath{\gamma}}$ phases in which the $\ensuremath{\gamma}$ value ranges from $\ensuremath{\sim}1.70$ to 1.75.

Tsuyoshi Kajitani

Papers

The new neutron powder diffractometer with a multi-detector system for high-efficiency and high-resolution measurements

Low-Temperature Thermoelectric Properties of the Composite Crystal [Ca 2CoO 3.34] 0.614[CoO 2]

Modulated Structure of the Thermoelectric Compound [Ca2CoO3]0.62CoO2

Preparation of Bi2Te3 films by electrodeposition

Modulated crystal structure of chimney-ladder higher manganese silicides MnSi γ (γ∼1.74)