Rapid Oscillations in (TMTSF)2PF6

In order to clarify the origin of the “Rapid Oscillation” (RO) in (TMTSF)₂PF₆, we studied the magnetoresistance anisotropy in the Field-Induced Spin Density Wave (FISDW) phase. We have found that in the FISDW insulating state, the Fermi surface is not totally gapped; the remaining 2D metallic pockets are quantized in magnetic field and give rise to the RO. Decreasing temperature does not change the size and orientation of the closed pockets, rather, it causes depopulation of the delocalized states in favor of the localized ones, resulting in the disappearance of the RO.     

Anisotropic SDW Dynamics in (TMTSF)2PF6

The anisotropic transport properties of the spin-density-wave model-com- pound (TMTSF)₂PF₆ have been studied by dc and microwave methods. According to mean-field theory, the activation energy in the SDW state below T_SDW = 12 K is approximately 20–25 K in all directions when measured by dc methods. Microwave experiments along the a, b′ and c* axes reveal that the collective transport, which is considered to be the fingerprint of the spin-density-wave condensate, is present in the a and b′ directions, but not along the least conducting c* axis. In contrast to common quasi one-dimensional models, the density wave also slides in the perpendicular b′ direction. Can this behavior be explained by the nesting properties of the quasi one-dimensional conductor?     

Long-Time Heat Release in the Quasi-1D Conductor (TMTSF)2PF6 at Low Temperatures

We have measured the heat capacity and the heat release of the quasi-1D conductor (TMTSF)₂PF₆ in its spin-density wave ground state. Below 1K the presence of low-energy excitations is at the origin of slow heat release over time scales from about 1s up to 10⁵s. In a first attempt, we analyzed this behaviour with a modified version of the standard tunneling model used in the case of amorphous solids, introducing a short-time cut-off in the distribution of the relaxation times of tunneling states. A remarkable feature of the heat release in (TMTSF)₂PF₆ is its high absolute value, which is 3–4 orders of magnitude larger than in structural glasses. The heat capacity contains a Schottky and a quasi-linear term.     

Magnetic Field Influence on the Low Temperature Heat Capacity and Heat Release of (TMTSF)2PF6

We have measured under applied magnetic field the heat capacity c _p and heat release of the quasi-1D conductor (TMTSF)₂PF₆ in its spin density wave (SDW) ground state. The low-temperature heat capacity (T < 0.5 K) is dominated by a Schottky anomaly contribution. A corresponding term was also found for the heat release. In this T-range both properties are strongly sensitive to moderate magnetic fields (i.e., below 0.5 T): their amplitudes have a sharp maximum for H _c=0.2 T. We show that the corresponding density of two-level states N _S undergoes a sharp maximum at H _c, which rules out an extrinsic origin for the two-level states. Instead we suppose an intrinsic origin, such as defects of commensurability of the SDW, as the (slow) excitations related to the domain walls. This effect is found to be independent on the field orientations H a and H a.     

Coexistence of Quasi-One- and -Two-Dimensional Electronic Structures in (EDO-TTF)2X (X = GaCl4, ReO4)

Crystal structures and physical properties of (EDO-TTF)₂X where EDO-TTF = ethylenedioxytetrathiafulvalene, X = GaCl₄ and ReO₄ were investigated. These isostructural salts belonged to triclinic system with space group P1, and two kinds of the donor layers coexisted in a crystal. EDO-TTF formed head-to-tail and head-to-head type columnar structures in each donor layer, for which quasi-one- and -two- dimensional Fermi surfaces were calculated, respectively.     

Sonochemical fabrication and characterization of ceria (CeO2) nanowires

Ceria (CeO2) nanowires have been successfully synthesized by a sonochemical method in ambient air and alkali aqueous solution from CeO2 nanoparticles without using any templates. The results showed that both alkali concentration and ultrasonic irradiation played critical roles in the formation of the nanowires. The crystalline structure and dimensions of the nanowires were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The UV-visible absorption spectrum result showed that the products had conspicuous shape-specific effect. Microstructural analysis in HRTEM revealed that the preferential growth direction of CeO2 nanowires was [110]. Moreover, the catalytic activity of Au/CeO2 using CeO2 nanowires as support for CO conversion was higher than that obtained using bulk CeO2 as support.     

Evidence for the π-d Interaction Comparing Magnetoresistance in (EDT-DSDTFVO)2 X, X=FeCl4, GaCl4

Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)₂ClO₄ for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)₂ClO₄.     

Low Temperature Study of the Mixed Donor System (TMTSF1-x TMTTF x )2PF6 : Crystal Structure, ESR and Transport Property

The phase diagram of the mixed donor quasi one-dimensional (Q1D) metallic system (TMTSF_1-x TMTTF _x )₂PF₆ has been studied. The study on the mixed donor systems helps us to establish not yet clarified phase boundaries in the Q1D system. We showed dependencies of properties on the donor mixing percentage for crystal parameters, resistivity, ESR(intensity and line width). ESR results show clear changes in the susceptibility and line width around 40 K. This result may indicate the existence of new boundary determined by the microscopic method on the Q1D phase.     

Phase Stability of the A2Cu3O4X2 (A = Alkaline-Earth; X = Halogen) System

Stability of A ₂ Cu ₃ O ₄ X ₂ (A = Sr, Ba; X =Cl, Br) of the 2342 phase with the Cu ₃ O ₄ plane, which is composed of the Cu(1)O ₂ and extra Cu(2) sublattices, has been studied in the temperature range between 600 °C and 950 °C. Polycrystalline samples of the composition Sr _2–x Ba _x Cu ₃ O ₄ Cl _2–y Br _y were prepared by the solid-state reaction method. From the powder x-ray diffraction analysis, we have made the phase diagram (x vs. y vs. heat-treatment-temperature). It has been found that the 2342 phase becomes stable with increasing x and y at high heat-treatment-temperatures instead of a mixture of CuO and the A ₂ CuO ₂ X ₂ (2122) phase with the CuO ₂ plane. These results can be explained in terms of the structural matching between the Cu ₃ O ₄ plane and the A ₂ X ₂ layer.     

Electrochemical fabrication of Sn nanowires on titania nanotube guide layers

We describe a novel approach for the fabrication of tailored nanowires using a two-step electrochemical process. It is demonstrated that self-organized TiO(2) nanotubes can be used to activate and guide the electrochemical growth of Sn crystallites, leading to the formation of vertical features with a high aspect ratio. We show that the dimensions and the density of Sn crystallites depend on the electrodeposition parameters.     

Electrochemical fabrication of SrTiO3 nanowires with nanoporous alumina template

Strontium titanate nanowires were electrochemically synthesized with nanoporous alumina template. Both chemical and electrical variables such as electrolyte pH, temperature, and current waveform were modulated to investigate the synthesis process of SrTiO3 nanowires. Superimposed cathodic pulse and diffusion time accelerated the growth of SrTiO3 nanowires, which suggested that the concentration of H+ and Sr2+ ion inside alumina template had a strong influence on the formation of SrTiO3 nanowires. Morphology and crystallinity of SrTiO3 nanowires were investigated with scanning electron microscope, X-ray diffractometer and energy dispersive X-ray spectroscopy.     

Organic metal (EDO-TTF)2PF6 with multi-instability

Abstract

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.     

Organic metal (EDO-TTF)2PF6 with multi-instability

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.     

Synthesis and crystal structures of a new (2,3-(CH3)2C6H3NH3)H2XO4 (X=P,As)

The aim of encapsulation of 2,3-dimethylanilinium cation in (H₂XO₄)_n polymeric anion chains is to build acentric frameworks that are efficient for non-linear optical (NLO) applications. The synthesis and structures of two new inorganic–organic NLO crystals with general formula (2,3-(CH₃)₂C₆H₃NH₃)H₂XO₄ (X=P, As) are reported. The magnitude of their second harmonic generations (SHG) responses was found to be between the KDP and urea. They crystallize with monoclinic unit-cells and are isotopic. We have determined the structure of phosphoric salt. The following unit-cell parameters were found: a=8.866(3) Å, b=5.909(6) Å, c=10.644(5) Å, β=112.44(1)°, V=515.5(5) Å³ and D_X=1.412 g cm⁻³. The space group is P2₁ with Z=2. The structure was refined with R=0.041 (R_w=0.057) for 1652 reflections with I≥3σ(I). It exhibits infinite (H₂PO₄)_nⁿ⁻ chains. The organic groups (2,3-(CH₃)₂C₆H₃NH₃)⁺ are anchored between adjacent polyanions through multiple hydrogen bonds. Chemical preparation, crystal structure, calorimetric and spectroscopic investigation are described.     

Thermal expansion of TlInX2 (X = S, Se, Te)

The thermal expansion coefficients of THnS₂, TlInSe₂, and TlInTe₂ were measured in the range 77– 350 K. The data for both single-crystal and polycrystalline TlInS₂ were found to exhibit features attributable to ferroelectric and commensurate-incommensurate phase transitions. The measured thermal expansion coefficients of THnS₂, TlInSe₂, and TlInTe₂ were used to calculate the Debye temperatures and root-mean-square dynamic atomic displacements. In going from TlInS₂ to TlInSe₂ and to TlInTe₂, the Debye temperature increases and the root-mean-square atomic displacement decreases, which can be attributed to the increase in bond ionicity.