Tsukio Ohtani

Synthesis of binary copper chalcogenides by mechanical alloying

Copper sulfides (tetragonal Cu{sub 1.92}S-Cu{sub 1.99}S, rhombohedral Cu{sub 1.71}S-Cu{sub 1.89}S, CuS) selenides ({beta} Cu{sub 2{minus}x}Se, Cu{sub 3}Se{sub 2}, {gamma} CuSe, CuSe{sub 2}), and tellurides (Cu{sub 2{minus}x}Te, Cu{sub 3}Te{sub 2}) were prepared from mixtures of the elements by mechanical alloying (MA), using a high-energy ball mill. The compounds were obtained by 60--120 min of MA. It is notable that two metastable high-pressure phases were obtained by MA: tetragonal Cu{sub 2{minus}x}S and pyrite-type CuSe{sub 2}. The tetragonal phase gradually transformed to the stable phase of djurleite when kept at room temperature. Cu{sub 1.71}S-Cu{sub 1.89}S also formed a metastable rhombohedral phase.

Synthesis of copper, silver, and samarium chalcogenides by mechanical alloying

Abstract CuIn X 2 ( X = S , Se , Te ), Ag 2 S, Ag 2 Se, Ag 3 Te 2 , Ag 1.9 Te, AgCuSe, Sm 3 Se 4 , Sm 2 Se 3 , and SmTe were synthesized by a mechanical alloying method, using a high-energy planetary ball mill. The compounds were obtained by milling mixtures of the elements with desired ratios in agate or Cu-Be vials for 60–180 min.

Preparation and magnetic properties of the new ternary chalcogenides isotypic with TlV5S8 and TlV6S8

Abstract New ternary chalcogenides isostructural with TlV5S8 and TlV6S8 were synthesized directly from the elements: InTi5Se7.8, RbV5S7.8, KCr5Se7.8, InCr5Se7.8, TlCr5Te7.8, KTi6Se7.8, KV6S7.8, RbV6S7.8, InV6S7.8, and Tl1.4V6 (Se6.8P1.0). Magnetic susceptibility measurements for these compounds were performed from 77 K to a room temperature. TlCr5Te7.8 was found to be a ferromagnet with a Curie temperature of about 150 K. The results of the deintercalation of thallium of TlV5Se7.8 also are reported.

Physical properties and phase transitions of β Cu2-xSe (0.20≤x≤0.25)

Abstract β-Cu2−xSe (0.20≤x≤0.25) showed a transition to a two-phase mixture of (α+β) at ∼250 K, and then the β phase transformed to an ordered new phase at 180 K. The 180 K transition is characterized by the jump of electrical resistivity ρ, Hall coefficient RH, Seebeck coefficient S and magnetic susceptibility χ on cooling. Measurements of RH and S revealed that the phase below 180 K is a degenerate p-type semiconductor, where the holes originate from the deficient copper atoms. The phase above the 180 K transition showed the two-band conduction of majority holes and minority electrons. Magnetic susceptibility measurements showed that the compound is a diamagnet above ∼180 K, and a paramagnet below ∼180 K.

Electrical Properties of Ni1-xS

Hexagonal nickel sulfide NiS shows a metal-nonmetal transition with the appearance of antiferromagnetism as temperature is lowered below 265 K ( T t ). Measurements of conductivity, Hall coefficient, thermoelectric power and magnetoresistance were made on polycrystalline samples of hexagonal Ni 1- x S (0.004≦ x ≦0.050). The low temperature phase is found to be a degenerate semiconductor with a high hole density from 3.13×10 20 cm -3 ( x =0.004) to 1.60 ×10 21 cm -3 ( x =0.020), which is essentially due to ionized nickel vacancies. Carriers are mainly scattered by ionized and neutral impurities associated with nickel vacancies. The effective mass is estimated from Seebeck coefficients to have a value between 1.50 m 0 and 2.90 m 0 . Above T t , the compound is a normal metal without a magnetic moment. The low temperature resistivity has revealed the Debye temperature to be 175 K for the metallic phase. There is no apparent evidence of a strong correlation effect although the electronic state densities are l...

The phase study of the TlVS system and the properties of TlV6S8 and TlV5S8 phases

The ternary phase diagram of the TlVS system was investigated using samples quenched from 400°C, especially in the neighborhood of TlV6S8 and TlV5S8 phases. The TlV6S8 phase (TlxV6Sy) exists between 0.75 < x < 1.00 and 7.55 < y < 7.90, and the TlV5S8 phase (Tlx′V5Sy′) between 0.70 < x′ < 1.00 and 7.54 < y′ < 7.98. A new ternary phase with the nominal composition of TlV2S4 was found in addition to the three known ternary phases. The entirely deintercalated V6S7.8 with the framework structure was obtained by using 1 N AlCl3 + 0.01 N FeCl3 aqueous solution, while the lower phase limit of the TlV5S8 phase was Tl0.33V5S8 consistent with the earlier work. The electrical resistivity and the magnetic susceptibility measurements show that these compounds are expected to be weakly magnetic itinerant-electron systems.

Nuclear Relaxation Study in Strong Coupling Superconductors –A Comparison with High-T c Superconductors–

The nuclear relaxation behavior in s - wave superconductors has been investigated as for Chevrel-phase superconductors, TlMo 6 Se 7.5 and Sn 1.1 Mo 6 Se 7.5 with T c =12.2 K and 4.2 K, respectively. The nuclear-spin-lattice-relaxation rate, 1/ T 1 , of 119 Sn in Sn 1.1 Mo 6 Se 7.5 reveals a distinct coherence peak just below T c , followed by an exponential decrease with the isotropic energy gap of 2Δ=3.6 k B T c in a weak coupling regime. By contrast, 1/ T 1 of 205 Tl in TlMo 6 Se 7.5 possesses no coherence peak, although the exponential decrease of 1/ T 1 has also been observed with a somewhat larger value of 2Δ=4.5 k B T c in a strong coupling regime. The stronger electron-phonon coupling enhances the superconducting transition temperature and at the same time, opens a decay channel to cause an intense damping of quasiparticles, resulting in the depression of the coherence peak. The comparison with high- T c superconductors will be discussed.

Synthesis, order-disorder transition and magnetic properties of LiLnS2, LiLnSe2, NaLnS2 and NaLnSe2 (Ln=Lanthanides)

Abstract Ternary chalcogenides LiLnS 2 , LiLnSe 2 , NaLnS 2 , and NaLnSe 2 (Ln-La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, or Y) were prepared by heating the mixtures of elements. DTA(differential thermal analysis) measurements showed the first order transitions at high temperatures above 600 °C in LiLnS 2 (Ln=Dy, Ho, Er, Y), LiLnSe 2 (Ln=Gd to Er), NaNdS 2 , and NaCeSe 2 , which are considered order-disorder transitions between a NaCl and an α-NaFeO 2 structure. This is consistent with X-ray diffraction measurements. Magnetic susceptibility measurements revealed that all the lanthanides ions are in trivalent state.

Properties of a new nanosized tin sulphide phase obtained by mechanochemical route

Abstract The paper deals with the properties of a new 4H-SnS2 phase (N-phase) synthesized together with berndtite 4H-SnS2 by a mechanochemical route from elemental tin and sulphur. The surface and bulk properties of SnS2 phases were verified by surface area measurements, particle size analysis, electron microscopy, XRD, Mossbauer spectroscopy and chemical dissolution methods. The particles of synthesized product are 12–18 nm in size and during milling, secondary particles (aggregates) are formed that are 20–60 μm in size. The particle size and a high developed surface area (7–21 m2 g−1) greatly influence the solid–liquid reaction and solid transformations of mechanosynthesized tin sulphide products.

Synthesis of new ternary tunnel chalcogenides by ion exchange reactions and deintercalation of the ternary chromium selenides

Many ternary tunnel chalcogenides with TlV5S8 and TlV6S8 structures were prepared by ion exchange reactions: TlM5X8 + AI (or ABr) → AM5X8 + TlI (or TlBr), and TlM6X8 + AI (or ABr) → AM6X8 + TlI (or TlBr), where M = Ti, V, and Cr, X=S, Se, and Te, and A=Na, K, Rb, and Cs. The compounds newly obtained are CsxV5S8, ATi5Se8 (A=Na, K, Rb, and Cs), AV5Se8 (A=K, Rb, and Cs), ACr5Se8 (A=Na, Rb, and Cs), ACr5Te8 (A=K, Rb, and Cs), AV6S8 (A=Na and Cs) and Ati6Se8 (A = Na, Rb, and Cs). TlxCr5Se8 (0.33≤x<1.0) was prepared by deintercalation method. The magnetic susceptibility (χ) measurements showed TlxCr5Se8 (x=0.65 and 1.0) to be an antiferromagnet with Neel point at 52 K. Effective magnetic moment Peff (μBCr atom) in TlxCr5Se8 was close to that of Cr3+ and was essentially invariable with x, suggesting the charge of host matrix [Cr5Se8 is constantly −1.