Production and microwave spectra of dithioformic acid,HCSSH

Hitherto unknown dithioformic acid, HCSSH, has been produced by pyrolysis (300°C) of methanetrithiol, HC(SH)₃, and identified by the microwave spectrum (18–40 GHz) of its most abundant species H¹²C³²S³²SH. Rotational transitions of this species in its ground state have been assigned to a trans and a cis rotamer. Both rotamers are planar, the trans conformer being the more stable by ca. 350 cm^?1 mole^?1. For each rotamer spectra of molecules in two vibrationally excited states have been assigned. Frequencies of transitions of importance for search for HCSSH in interstellar space are reported.     

Iterating ordinal definability

The paper presents a uniform way of obtaining by forcing descending sequences of the iterations of HOD and describes their structure. Among other things the following results are proved:Theorem. Any model M of ZFC can be obtained by the transfinite iteration of HOD in some generic extension N of M, i.e. M=(HOD^On)^N.Theorem (ZFC). For any ordinal α there is a complete Boolean algebra B with a decreasing sequence of derivatives of length α.Moreover some other results about ordinal definability are reproved using the introduced method. This method is a refinement of the classical method of coding introduced by McAloon in [11].     

Electrical properties and defect chemistry of TiO2 single crystal. I. Electrical conductivity

The present work reports the electrical properties of high-purity single-crystal TiO(2) from measurements of the electrical conductivity in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities in the range 10(-13) to 10(5) Pa. The effect of the oxygen activity on the electrical conductivity indicates that oxygen vacancies are the predominant defects in the studied ranges of temperature and oxygen activities. The electronic and ionic lattice charge compensations were revealed at low and high oxygen activities, respectively. The determined semiconducting quantities include: the activation energy of the electrical conductivity (E(sigma) = 125-205 kJ.mol(-1)), the activation energies of the electrical conductivity components associated with electrons (E(n) = 218 kJ.mol(-1)), electron holes (E(p) = 34 kJ.mol(-1)), and ions (E(i) = 227 kJ.mol(-1)), and the enthalpy of motion for electronic defects (DeltaH(m) = 4 kJ/mol). The electrical conductivity data are considered in terms of the components related to electrons, holes, and ions. The obtained data allow the determination of the n-p demarcation line in terms of temperature and oxygen activities. The band gap determined from the electronic component of the electrical conductivity is 3.1 eV.     

Electrical properties of niobium-doped titanium dioxide. 1. Defect disorder

The present work reports the electrical conductivity and thermoelectric power for Nb-doped TiO(2) at elevated temperatures (1073-1298 K) in the gas phase of controlled oxygen activity, 10(-14) Pa < p(O(2)) < 75 kPa. It is shown that in reduced conditions the Nb-doped TiO(2) exhibits metallic-type conductivity. This finding paves the way for the development of high-performance photoelectrodes with substantially reduced internal energy losses during charge transport. The present work also determined the equilibrium constant for the formation of oxygen vacancies and titanium vacancies for Nb-doped TiO(2).     

Electrical properties and defect chemistry of TiO2 single crystal. II. Thermoelectric power

The present work reports the thermoelectric power of high-purity single-crystal TiO(2) in the temperature range 1073-1323 K and in gas phases of controlled oxygen activities, p(O(2)), in the range 10(-13) to 7.5 x 10(4) Pa. The thermoelectric power versus log p(O(2)) dependence for strongly reduced TiO(2) at p(O(2)) < 10(-5) Pa may be approximated by a slope of 1/6, which is consistent with the defect disorder governed by electronic charge compensation of oxygen vacancies. The thermoelectric power data confirm that oxygen vacancies are the predominant ionic defects. These data indicate that TiO(2) at high p(O(2)) exhibits p-type properties. It is shown that the p(O(2)) related to the n-p transition increases with increase of temperature.     

Electrical properties of niobium-doped titanium dioxide. 2. Equilibration kinetics

The present work reports isothermal gas/solid equilibration kinetics for Nb-doped TiO(2) (0.65 atom %) at elevated temperatures (1073-1298 K) within narrow ranges of oxygen activity spanning between 10(-13) Pa and 75 kPa. The equilibration kinetics were monitored using electrical conductivity measurements. The kinetic data were used to determine the chemical diffusion coefficient (D(chem)). D(chem) as a function of p(O(2)) exhibits a complex dependence, which is considered in terms of defect disorder and the related concentrations of electronic charge carriers. The activation energy of D(chem) in the p(O(2)) range 10 Pa < p(O(2)) < 75 kPa varies in the range 88.0-98.2 kJ/mol. It is important to note that the chemical diffusion coefficient in strongly reduced conditions [p(O(2)) = 10(-9) Pa] exhibits a negative temperature dependence of D(chem) (-67.2 kJ/mol). This finding indicates that under these conditions transport in a chemical potential gradient is consistent with metallic charge transport.     

Defect disorder of titanium dioxide

The present work derived defect disorder diagram representing the effect of oxygen activity on the concentration of both ionic and electronic defects for undoped TiO2. This diagram was determined using the equilibrium constants derived in the present work, including (i) the intrinsic electronic equilibrium constant, (ii) the equilibrium constant for the formation of oxygen vacancies, and (iii) equilibrium constant for the formation of titanium vacancies. These equilibrium constants are consistent with three properties determined independently, including: electrical conductivity, thermoelectric power and change of mass determined by thermogravimetry. The derived defect disorder diagram may be used for tailoring semiconducting properties of TiO2 that are desired for specific applications through the selection of optimized processing conditions.