Tian Mingliang

Fractal formation and tunnelling effects on the conductivity of Au/a-Ge bilayer films

The fractal crystallization of the Au/a-Ge bilayer films has been investigated, and the resistance characteristics have been first measured by the two-probe configuration method. The experimental results suggest that the resistance R of various annealing films are influenced by the fractal formation and the fractal dimension. These phenomena were explained by the Random Tunnelling Junction Network (RTJN) model.

Two-dimensional hole localization induced by Zn, Ni, and Mg dopings in Cu sites in La1.85Sr0.15Cu1-xMxOy

Samples of La1.85Sr0.15Cu1-xMxOy(M = Ni, Zn, and Mg) with a wide range of dopant concentration (0≤x≤0.30) were synthesized. X-ray diffraction analysis shows that the Zn doping results in a tetragonal-orthorhombic transition asx- >0.15. while both Ni- and Mg-doped samples still remain tetragonal up tox = 0.3. Furthermore, the Ni, Zn, and Mg dopings all reduce the local Jahn -Teller distortion of the CuO6 octahedron in a similar way. The metalinsulator transition at the region of higher doping levei (x> 0.1) is observed in all three doped systems. The observed metal-insulator transition can be well interpreted in the context of Anderson’s theory of disorder-induced localization. For most of the semiconducting-like samples with higher doping level (x> 0.1), the conductive behavior is dominated by two-dimensional variable-range-hopping (2D-VRH) with {ie-13-01} This suggests that all the dopings of Ni, Zn, and Mg in Cu sites cause the localization of the holes. In addition, a remarkable difference in the room-temperature resistivity for the heavily doped samples with the same dopant (Zn, Ni, Mg) concentrations is also observed. A possible explanation is provided for this phenomenon.

The temperature dependence of resistivity and thermoelectric power in lanthanum molybdenum oxide crystal

Electrical resistivity, voltage - current (V - I) characteristics and thermoelectric power (TEP) at various temperatures in the quasi-two-dimensional single crystal were measured. It was found that at 130 K the resistivity shows a metal - semiconductor transition, and the TEP has a minimum value. In the semiconducting states below 130 K, the electronic transport presents a clear non-linear behaviour. By analysis of the above data, it is indicated that above 130 K the crystal is a metal and electrons are dominant carriers; below 130 K the crystal becomes a semiconductor with a small energy gap, the two types of carrier being possibly co-existent. The anomalies of TEP and resistivity near 130 K may be associated with the formation of so-called charge-density waves due to the partial opening of a gap.

Thermoelectric Power of Al Doped La–Sr–Cu–O System

The normal-state transport properties of La1.85−xSr0.15+xCu1−xAlxOy system have been investigated by means of resistivity and thermoelectric power. The structural analysis indicates that with the increase of x, both the lattice parameter a and c decrease. An MI transition appears with Al doping. Al doping partly perturb the periodic potential of the system, thus producing a weakly temperature dependent TEP. The different effect of doping between Al and other transition metal is discussed.

Thermoelectric power of the La214 system doped with trivalent metals (Fe, Ga, Co, Cr, Mn, and Al)

The thermoelectric power (TEP) of the La214 system doped with trivalent metals (Fe, Ga, Co, Cr, Mn, and Al) was investigated systematically. The TEPs for the samples doped with 3d metals and sp metals show different temperature-dependent behaviours. The broad maximum in the S(T)-T curve notably shifts to higher temperature upon 3d-metal (Fe, Co, Mn, and Cr) doping, while for the sp-metal (Ga and Al) doping, the broad peak is nearly unchanged. Magnetic scattering is proposed as the main factor influencing the TEP. Other possible factors are analysed and discussed in this paper.

The anomalous thermoelectric power of the La doped Bi-2201 phase

Samples of the system with different oxygen contents have been obtained by annealing the as-grown samples at different temperatures and oxygen partial pressures. The results of resistivity and thermoelectric power (TEP) measurements of these samples are reported here. Some anomalous phenomena in transport for the underdoped sample of were observed, i.e., below a characteristic temperature, the TEP exhibits a significant enhancement and the temperature dependence of the resistivity deviates downward from linearity. These results imply that a spin gap exists in the La doped Bi-2201 system. By comparison with the results reported previously, we suggest that the microstructural characteristics are another important factor in determining the spin excitation spectrum.

A study on the transport properties in the system

Samples of the (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.6) system with different oxygen concentration are obtained. The analysis of x-ray diffraction indicates that a tetragonal - orthorhombic transition takes place with increase of Pb content. The resistivity measurement shows that for the quenched samples the highest is 35 K, and (zero resistivity) is 25 K; while for the samples annealed under low oxygen partial pressure, the highest and increase to 45 K and 37 K, respectively. Moreover, the phenomenon of a spin gap is systematically observed in this system. The analysis of the experimental results reveals that the microstructural characteristic of the Bi2201 system is closely related to both the spin-paring and superconductivity. The dominated spin scattering mechanism is suggested as the origin of the T-linear resistivity.

Relation of Oxygen Content and Modulation Structure in Bi2201 System

Two series of samples of Bi1.8Pb0.2Sr2CuOy and Bi1.9Sr1.6La0.4CuOy systems with different oxygen content were prepared. The microstructure of these samples was investigated by means of X-ray diffraction (XRD) and electron diffraction (ED). The analysis of XRD indicates that a progressive change in lattice parameters takes place with the removal of oxygen. The analysis of ED patterns reveals that for the Bi1.8Pb0.2Sr2CuOy system, the orthorhombic modulation (Pb-type modulation) is strongly related to the oxygen in Bi2O2 layers, which implies that the orthorhombic modulation is not compositional (Pb) modulation, and the periodic distribution of oxygen in Bi2O2 layers induced by Pb doping may be the real origin of orthorhombic modulation. While for the Bi1.9Sr1.6La0.4CuOy system, the monoclinic incommensurate modulation is independence of the variation of oxygen in Bi2O2 layers, which suggests that the intercalation or removal of extra oxygen atoms was only the result of the monoclinic modulation structure changing, and the crystal misfit between Bi2O2 layers and perovskite blocks was the real driving force of the Bi-concentrated band superstructural modulation.

Study of the microstructure and normal-state transport properties in the Bi1.9Sr1.6La0.4CuOy system

Abstract The samples of Bi 1.9 Sr 1.6 La 0.4 CuO y with different oxygen concentrations are obtained by annealing the sintered sample in different conditions. The analysis of lattice parameters shows that the removal of oxygen from the system results in an orthorhombic-tetragonal transition. The analysis of the electron diffraction patterns revealed that the incommensurate modulation structure is independent of the oxygen content, which is in disagreement with the extra oxygen model. In the resistivity measurement, an anomalous deviation of resistivity downward from T -linearity at 180 K is detected, and a corresponding anomaly in thermoelectric power (TEP) is also found, which suggests that a spin gap exists in the Bi-2201 system. The comparison of microstructural characteristics for different samples demonstrates that the structural factor has crucial influence on the spin excitation spectrum.

OHMIC RESISTIVITY AND NONLINEAR TRANSPORT OF CHARGE DENSITY WAVES IN BLUE BRONZES K0.3MoO3

Ohmic resistivity and nonlinear transport properties of sliding charge density wave (CDW) conduction in blue bronze K0.3MoO3 were measured. It is found that at about 183 K the sample undergoes a metal-to-semiconductor transition, i.e. Peierls transition. In semiconducting CDW state, the estimated activation energies eg in the temperature ranges of 77–135 and 150–180 K are, respectively, about 0.033 and 0.051 eV by the measurements of ohmic resistivity, where the field is below the depinning field VT of CDW motion. Above VT, the analytic form of nonlinear current of sliding CDW in a moderate current range fits the power law relation, i.e. ICDW∝(V/VT−1)α; the exponent a is not a constant, but relies on temperatures. In high field range, the analytic form of nonlinear current of the CDW motion deviates from the power law relation, but it can be described by the microscopic model including the internal degrees of freedom proposed by Sneddon et al., i.e. ICDW=σnE+CE1/2, with σn being the conductivity of normal...