Micro‐Scale Device—An Alternative Route for Studying the Intrinsic Properties of Solid‐State Materials: The Case of Semiconducting TaGeIr

An efficient application of a material is only possible if we know its physical and chemical properties, which is frequently obstructed by the presence of micro‐ or macroscopic inclusions of secondary phases. While sometimes a sophisticated synthesis route can address this issue, often obtaining pure material is not possible. One example is TaGeIr, which has highly sample‐dependent properties resulting from the presence of several impurity phases, which influence electronic transport in the material. The effect of these minority phases was avoided by manufacturing, with the help of focused‐ion‐beam, a μm‐scale device containing only one phase—TaGeIr. This work provides evidence for intrinsic semiconducting behavior of TaGeIr and serves as an example of selective single‐domain device manufacturing. This approach gives a unique access to the properties of compounds that cannot be synthesized in single‐phase form, sparing costly and time‐consuming synthesis efforts.     

A Structural Investigation of Ga3−xIn5+xSn2O16

The structure of the recently reported transparent conductor, Ga_3−xIn_5+xSn₂O₁₆(0.3<x<1.6), was established by a combination of high-resolution electron microscopy, convergent-beam electron diffraction, and Rietveld analysis of powder diffraction data (X-ray and time-of-flight neutron methods). This “T-phase” compound has an anion-deficient fluorite-derivative structure whose space group isI4₁/a. Although there are similarities to the parent oxide structures, the T-phase lacks one of the distorted InO₆octahedra observed in In₂O₃, which may account for its inability to be donor-doped by Sn.     

Thermodynamics of the movable oxygen and conducting properties of the solid solution YBa2Cu3-xCoxO6+δ at high temperatures

High precision coulometric measurements of the equilibrium oxygen content in the solid solution YBa₂Cu_3-xCo_xO_6+δ, where x=0, 0.2, 0.4, 0.6 and 0.8, were carried out using a double-cell technique in the temperature range 600 – 850 °C and at oxygen pressure varying between 10⁻⁵ and 1 atm. The data were employed to determine the partial molar enthalpy and entropy of the movable oxygen depending on δ and x. The electrical conductivity and thermopower were also measured in the same range of the external parameters, and their dependence on the oxygen concentration was determined at different cobalt content. The data reveal several types of oxygen sites participating in the gas-solid equilibrium. The behavior of thermodynamic functions is indicative of the partial ordering of the complex species which form the structural layer Cu_1-xCo_xO_δ with variable content of oxygen and cobalt. It was shown that replacement of copper by cobalt does not result in appearance of the electronic charge carriers. The behavior of the thermopower and electric conductivity was explained with a narrow band model. The energy change with δ and x of the p-band, which dominates the conductivity, was found to follow the respective change in the oxygen partial enthalpy. Thus, electronic carriers in the layered structure of the cuprate are strongly influenced by the labile oxygen ions. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Structure and magnetic properties of Pb2Cu3B4O11: a new copper borate featuring [Cu3O8]10- units

Pb2Cu3B4O11 crystallizes in the monoclinic space group P2/n (No. 13) with a = 6.8016(15) A, b = 4.7123(10) A, c = 14.614(3) A, beta = 97.089(3) degrees, and Z = 2. The crystal structure consists of infinite [Cu3O8]10- zigzag chains of alternating dimers and monomers. The magnetic susceptibility and specific heat capacity show spin-gap and Curie-Weiss behaviors that can be explained by a model of Cu(2)-Cu(2) dimers and isolated or weakly coupled Cu(1) monomers.     

The Ag2O-V2O5-HF((aq)) system and crystal structure of alpha-Ag3VO4

Reactions between the three components Ag2O, V2O5, and HF(aq) were investigated under hydrothermal conditions, and the recovered phases were, in increasing Ag:V content, Ag2V4O11, beta-AgVO3, Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. A higher ratio of Ag2O to V2O5, as compared to a stoichiometric ratio, was required to synthesize Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. Owing to their solubility differences, the crystallization regions are not centered around the respective 2:1 and 3:1 Ag2O/V2O5 tie-lines but rather are centered along the 4:1 and 8:1 Ag2O/V2O5 tie-lines. Reactions with a 4:1 Ag/V ratio either resulted in Ag4V2O6F2 at 150 degrees C or Ag4V2O7 at 200 degrees C. Products were recovered in between 80% and 100% yield based on V2O5. Red transparent crystals of alpha-Ag3VO4 crystallize in the monoclinic space group C2/c, with cell parameters a = 10.1885(16) A, b = 4.9751(8) A, c = 10.2014(17) A, beta = 115.754(3) degrees .     

Ag4V2O6F2: an electrochemically active and high silver density phase

Low-temperature hydrothermal techniques were used to synthesize single crystals of Ag(4)V(2)O(6)F(2). This previously unreported oxide fluoride phase was characterized by single-crystal X-ray diffraction and IR spectroscopy and was also evaluated as a primary lithium battery cathode. Crystal data: monoclinic, space group P2(1)/n (No. 14), with a = 8.4034(4) A, b = 10.548(1) A, c = 12.459(1) A, beta = 90.314(2) degrees , and Z = 4. Ag(4)V(2)O(6)F(2) (SVOF) exhibits two characteristic regions within the discharge curve, an upper plateau at 3.5 V, and a lower sloped region around 2.3 V from reduction of the vanadium oxide fluoride framework. The material has a nominal capacity of 251 mAh/g, with 148 mAh/g above 3 V. The upper discharge plateau at 3.5 V is nearly 300 mV over the silver reduction potential of the commercial primary battery material, Ag(2)V(4)O(11) (SVO).     

Conductivity and carrier traps in La1−xSrxCo1−zMnzO3−δ (x=0.3; z=0 and 0.25)

Measurements of the equilibrium oxygen content, electrical conductivity and thermopower in the perovskite-like solid solution La_0.7Sr_0.3Co_1-zMn_zO_3−δ (z=0 and 0.25) as a function of the temperature and oxygen partial pressure are used to determine the temperature dependence of the conductivity and thermopower at different values of the oxygen deficiency. A model for a hopping conductor with screened charge disproportionation is applied for the data analysis in combination with trapping reactions of n- and p-type carriers on local oxygen vacancy clusters and manganese cations, respectively. Changes in the ratio of n-type to p-type mobility are due to variations in oxygen vacancy concentration and manganese content, while the energetic parameters governing charge disproportionation of the trivalent cobalt cations and formation of vacancy associates are shown to be essentially invariable. These calculated charge carrier site occupancies are used to model temperature variations of the electrical properties in La_0.7Sr_0.3Co_1−zMn_zO_3−δ in favorable correspondence with experimental observations.