Thermoelectric power of mixed electronic-ionic conductors II. Case of titanium dioxide

The purpose of the present work is the determination of the thermopower components corresponding to different charge carriers (electrons, electron holes and ions) for TiO₂ and the use of these data for evaluation of the effect of symmetry between these two properties. The procedure of the determination of these components was based on the following two approximations:

The first approximation is based on a symmetrical model assuming a consistency between thermopower and electrical conductivity within the n-p transition (minimum of electronic component of the electrical conductivity corresponds to zero value of the electronic component of thermopower).

The second approximation is based on the apparent asymmetry between thermopower and electrical conductivity within the n-p transition as determined from the first approximation.

The analysis, based on the data of the electronic components of thermopower and electrical conductivity for TiO₂ single crystal, results in the band gap (using the Jonker formalism). The determined band gap is equal to 2.77 eV and 2.57 eV at the first and the second approximations, respectively, while the band gap determined from the experimentally measured data is equal 3.35 eV. These values are consistent with the band gap determined from the data of electrical conductivity corresponding to the n-p transition point (E_g=3.16 eV) and for the data measured experimentally and those free of the ionic conductivity component (E_g=2.79 eV). The obtained results indicate that thermopower and electrical conductivity most likely exhibit the effect of symmetry.     

Dynamical enhanced electron emission and discharges at contaminated surfaces

Broad-area electrodes show electron emission already at electric field strengthsF≈10⁷ V/m. This enhanced field emission (EFE) occurs only for contaminated surfaces. EFE is accompanied by photon emission and gas desorption yielding finally discharges. EFE is caused by dust and contaminants initiating the following effects:

an electron is stochastically emitted in a trigger zone

the electron gains energyΔE?eΔxF ^*

which excites electronic states

which relax by the emission of electrons, photons, and atoms

where the positive charges left behind enhanceF ^*=βF (β?1) initiating so an electron avalanche, i.e., a high conductivity channel. Because of charge migration and neutralization, this avalanche has a life time. This pulsating EFE is accompanied by light emission and gas desorption yielding finally a gas cloud and a discharge.

The pulsating, self-sustained EFE has the same root as:

the enhanced secondary emission found first by Malter

the conductivity switching exhibited by thin (≈ 1 μm) layers of semiconductors or insulators

the normal cathode fall and

the firing-wave instability in neurodynamics.

     

Symmetrieeigenschaften achtkomponentiger Spinorfelder im Gitterraum

Starting from the four component Dirac equation for free particles without mass W.Heisenberg und W.Pauli have shown that the interaction term is uniquely defined, if one requires that all symmetries of free particles are preserved. Here we obtain similar results if we start from the eight component Dirac equation for free particles without mass:

1. The symmetry group of the eight component Dirac equation for free particles without mass has 16 parameters. It is isomorph to the direct product of the SU 4 and a one-parametric group: SU 4× (1).
2. The interaction operator is uniquely defined if one requires to preserve as many symmetries as possible of those given in (1).
3. But some of the symmetries in (1) are necessarily broken, in particular that of SU 3. The symmetry of the interaction operator is given by SO 4× (1)× (1).

These results mean:

1. The Heisenberg theory is uniquely defined, only if one assumes that the free particle part of the equation is well known.
2. The theory can be changed without modifying the fundamental idea ofHeisenberg andPauli to deduce an uniquely defined interaction operator if one starts with a modified free particle part.
3. A special kind of modification of the free particle part leads essentially to the SU 4-symmetry including that of SU 3, which is necessarily broken by the interaction term.
4. The question arises if this break of the SU 3-symmetry has something to do with the real break. This question is not yet touched in this paper.

     

Infrared and conductivity studies on blends of PMMA/PEO based polymer electrolytes

Poly(methylmetacrylate)/poly(ethylene oxide) (PMMA/PEO) based polymer electrolytes were synthesized using the solution cast technique. Four systems of PMMA/PEO blends based polymer electrolytes films were investigated:

1. PMMA/PEO system,
2. PMMA/PEO + ethylene carbonate (EC) system,
3. PMMA/PEO + lithium hexafluorophosphate (LiPF₆) system and
4. PMMA/PEO + EC + LiPF₆ system.

The polymer electrolytes films were characterized by Impedance Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The FTIR spectra show the complexation occurring between the polymers, plasticizer and lithium salt. The FTIR results give further insight in the conductivity enhancement of PMMA/PEO blends based polymer electrolytes.     

Photoemission on the highT c superconductors Y−Ba−Cu−O

XPS and UPS photoemission experiments on the highT _c superconductors (T _c ≈90 K) with nominal composition YBa₂Cu₃O_9-y (y≈2) show the following:

1. The density of electronic states at the Fermi energy is very small, much smaller than in pure Cu.
2. The Cu 2p spectra show only a Cu²⁺ contribution.
3. The Ba core levels show a structure with two components of nearly equal magnitude, which leads to the suggestion that these compounds have large O^2? vacancies coordinated to Ba²⁺ sites.
4. Annealing at 400°C under UHV conditions leads possibly to a partial reduction of Cu²⁺ to lower Cu valence states and to a small increase of the O^2? vacancy component of the Ba²⁺ line.

     

Polarization effects of picosecond CARS in liquids

Coherent Raman scattering of delayed probing pulses after ultrafast excitation is investigated under generalized polarization conditions. Three factors are shown to contribute to the scattering signal:

1. scattering off the isotropic part of the resonant material excitation via the isotropic component of the Raman polarizability
2. scattering via the anisotropic part of the Raman polarizability from a second, oriented component of the resonant material excitation
3. four-wave mixing via the non-resonant part χ_NR of the third-order susceptibility. We demonstrate theoretically and experimentally that different polarization conditions lead to drastic changes of the signal transients in liquids. For the ring breathing mode of C₆H₅Br the ratio of non-resonant to resonant contributions is measured to be χ_NR/χ_res=0.037±0.015.

     

The possibility of using a semiconductor thermal probe to investigate the power flow distribution in waveguides

Conclusions

1. The temperature profile of an absorbing film for a given microwave power flux distribution has been considered.
2. The conditions under which agreement is found between the temperature relief and the flux distribution has been clarified.
3. An experimental investigation has been carried out of the temperature profile in a matched film for the TE₁₀ mode.
4. The possibility of using a semiconductor thermal probe to investigate the microwave power flux distribution has been demonstrated.

     

Bestimmung von Stoßfrequenz und Stoßmodell in verschiedenen Flammenplasmen aus Absorption und Dispersion von Mikrowellen

The electron collision frequencies for four flames of different temperature and composition have been determined by means of measuring simultaneouslyX-band microwave attenuation and phase shift, which originate from the complex conductivity of the flame plasma. Hence the method can also be used for the determination of the collision frequencies of time dependent plasmas. In order to enhance the small magnitude of the quantities to be measured one hundred equal flames burnt inside the waveguide. The measurements show:

1. In flames collisions of electrons with induced dipoles dominate (Lorentz-theory).
2. The collision frequencies depend on the flame temperatureand on the chemical composition.

     

The moment of inertia at the saddle point of low energy fission of even-even nuclei

We use the molecular model of low energy fission, which describes the nucleus by two interacting fragments, to calculate the moment of inertia for U²³⁶ in the cranking approximation including BCS theory. We show that the moment of inertia at the saddle point:

1. depends almost linearly on the fragment distance.
2. is influenced only very weakly by the pairing constant and by the fragment deformations.
3. shows, as a function of the distribution of mass between the two fragments (A ₁ ,A ₂ ), a minimum near the magic configurationA ₁=132,Z ₁=50 and depends in this mass region strongly on the term structure near the Fermi energy.
4. is approximately that of a rigid body.

     

Small-angle X-ray scattering on spinodal,nucleotic or coarsening processes in two-phase systems containing spherical,fibrillar or lamellar inhomogeneities

We study the effects of some of the most important and typical structural changes in two-phase systems on selected structural parameters obtained from small-angle x-ray scattering (SAXS) measurements. To limit the present study, it was assumed that the Phase, 1, embedded in the matrix

1. is monodispersed and homogeneous,
2. possesses one of the three most extreme shapes (spherical, fibrillar or lamellar) and
3. changes its behaviour

1. through type change (spinodal or nucleotic or coarsening), without changing the shape,
2. through a change of the shape only, or
3. through a) (type change) and b) (shape change) simultaneously.

To find the type of change for three basically different shapes of Phase 1 and to calculate its intensity (amount of the change) the following three SAXS parameters must be compared before and after the treatment of the system:

1. chord lengthl ₁ (and/or radius of gyrationR),
2. volume partw ₁ of the Phase 1, and
3. relative inner surfaceS _v of the system.

It is shown by this comparison that by the pure type change in the case of

1. spinodal change, all three SAXRS parameters are increasing or decreasing simultaneously and proportional to a power of the intensity of the change,
2. nucleotic change,l ₁ (and/orR) is unchanged, the other two (w ₁ andS _v ) are increasing or decreasing simultaneously and directly proportional to the intensity,
3. coarsening change,w ₁ is unchanged and anincreasing ofl ₁ is always accompanied by adecreasing ofS _v and vice versa.

In addition to this type change, the cases of mere changes of the shape (“shape change”) and finally of simultaneous type and/or shape change are studied. For the case of pure shape change the alteration of the dimensions (chord lengthl ₁ and/or radius of gyrationR) must be followed. The limitations of the analyses of the simultaneous type and/or shape change are discussed in detail.     

Existence of phase transitions for quantum lattice systems

We prove that the following lattice systems:

1. anisotropic Heisenberg model,
2. Ising model with transverse magnetic field,
3. quantum lattice gas with hard cores extending over nearest neighbours,

exhibit phase transitions if the temperature is sufficiently low and the transverse (or kinetic) part of the interaction sufficiently small.     

Magnetostriction measurement by means of strain modulated ferromagnetic resonance (SMFMR)

A novel method for measuring magnetostriction constants is presented. A strain, periodic in time, applied to the sample, causes a modulation of the ferromagnetic resonance line position. The height of the signal obtained after phase-sensitive detection is proportional to the strain modulation depth. The appropriate magnetostriction constant λ is obtained by comparing the height of the SMFMR signal with that of the FMR line, as recorded by means of magnetic field modulation. Features of the new technique are:

1. high sensitivity: λ_min? 10_?9 forM=100 Oe and linewidth ΔH _d=1 Oe;
2. λ's belonging to distinct precession modes are separately determined;
3. applicable to thin layers for which strain gauge techniques cannot be used;
4. wide temperature range: 1.2 K<T<300 K;
5. uniform stress.

An illustrative example (YIG layer on GGG substrate) is given.     

Electronic and ionic conductivity in CaTiO3

The present work describes the electrical conductivity of undoped CaTiO₃ in terms of the electrical conductivity components corresponding to electrons, electron holes and ionic charge carriers in the temperature range 973 K — 1323 K and under controlled oxygen partial pressure (10 Pa — 72 kPa). These data are considered in terms of the transference numbers of the respective charge carriers. It appears that the ionic conductivity component assumes maximum at the n-p transition when the ionic transfer number reaches 50% of the total conductivity value at 1323 K. The present study also includes the determination of the activation energy of the conductivity component related to ions (162.1 kJ/mol), electrons (134.2 kJ/mol) and electron holes (86.2 kJ/mol). The data obtained in this work indicate that undoped CaTiO₃ exhibits a substantial level of ionic conduction that cannot be ignored in a quantitative analysis of electrical conductivity data.     

SIMS and flash desorption studies of nickel oxygen interaction

O₂ exposure of polycrystalline nickel at 300 K results in characteristics changes of secondary ion emission. These can be described by a model which is in good agreement with corresponding LEED, AES, XPS, and ΔΦ results of other authors. According to this model, oxygen can be bonded on Ni in at least five different phases:

1. chemisorption, indicated by a rapid increase of Ni⁺, Ni ₂ ⁺ , and Ni₂O⁺ (≦5 L);
2. a rearranged chemisorption layer, characterized by a drastic decrease of Ni⁺, Ni ₂ ⁺ , and Ni₂O⁺ (5–15 L);
3. nickel oxide (NiO) responsible for a strong NiO^?- and NiO ₂ ^? -emission (≦40 L);
4. oxygen on top of this NiO layer, producing a final increase of Ni⁺ and NiO⁺ and a O₂-flash signal at 400 K (>40 L);
5. bulk dissolved oxygen in thermal equilibrium with a chemisorption layer (after several exposure/heating cycles).

During ion bombardment of a 100 L O₂ exposed Ni surface these different binding states occur in a reversed order of succession. O₂-flash signals at 400 and 1100 K, related to drastic changes in secondary ion emission at 400, 700, and 1100 K, reflect the disappearance of various oxygen binding states. The exchange between different oxygen phases was studied by¹⁶O₂/¹⁸O₂ isotope experiments.     

Nachwirkungsmechanismen in Ferriten

In ferrites a large number of after-effects are found, with time constants between nano-seconds and years. In this review the after-effects due to ion-and electron motion will be treated. One finds:

1. single-ion effects in combination with lattice deformations, e.g. Mn³⁺;
2. ion effects caused by mobile vacancies, e.g. Co²⁺;
3. effects due to electron transfer:
4. Co²⁺?Co³⁺
5. Me²⁺?Fe³⁺, in combination with Me⁴⁺ and vacancies.
6. Me⁴⁺?Fe²⁺, with Me=Si, Ti (photomagnetic effect).

The electron transfer is found to be related to electrical effects. In analogy to the photoelectric effect, one has found that illumination produces changes in magnetic properties. Generally speaking, one has in ferrites as many problems with donors and acceptors as in other semiconductors. Information from magnetic measurements helps to elucidate their nature.     

Two-dimensional quantum field theories containing a massless scalar field

The following new findings are briefly reported:

1. A consistent quantum theory can be formulated for a free massless scalar field in two-dimensional spacetime.
2. Satisfactory operator solutions in terms of asymptotic fields can be constructed in the Thirring and Schwinger models.
3. Gauge invariance is spontaneously broken in the Thirring model as well as in the Schwinger model.

     

Spin-order and magnetic properties of BaZn2Fe16O27 (Zn2-W) hexagonal ferrite

We have observed large peaks in the ultrasonic attenuation of a pure and two doped LaAl₂ crystals in the temperature region of about 45 K which are possibly of the Bordoni type. Their most interesting characteristics are:

1. There is only one peak in each sample.
2. The peaks are so narrow that they can be described by the original Seeger model with only one actication energy and one attempt frequency.

     

Zur Dispersion der OberflÄchenplasmaverluste an reinen und oxydierten AluminiumoberflÄchen

The dispersion of the surface plasma oscillations is caused by

1. the coupling of the two surfaces of thin foils, that leads to a splitting into two modes of oscillation with different dependence of frequency on wavelength.
2. the influence of thin coating of e.g. oxide, that produces a displacement of the frequency depending on the wavelength of the surface oscillation.

Plasma oscillations were excited by 34 kV-electrons in thin foils of Aluminium vaporised on foils of Al₂O₃ in ultra-high vacuum. It was thus possible, to investigate oscillations of clean and oxidized Al-surfaces. By measurements of the energy loss as a function of the scattering angle of the exciting electrons both effects of dispersion could be demonstrated in good agreement with the theory. Also the influence of retardation was observed.     

Optically-pumped stimulated recombination radiation inp-type InSb in high magnetic fields

In this paper measurements of the frequency, linewidth and polarization of stimulated recombination radiation (SRR) fromp-type InSb are reported. The samples had low excess-carrier concentrations between 10¹⁴ and 10¹⁵ per cm³ and different lengths between 0.4 and 9 mm. They were held in magnetic fields up to 6T at temperatures of pumped liquid helium. The excitation was done optically by the radiation of a Q-switched CO-laser. We could observe a number of different stimulated processes:

1. band-to-band recombination (tuning between 1875 and 1980 cm^?1),
2. band-to-acceptor recombination (tuning between 1840 and 1930 cm^?1),
3. stimulated spin-flip Raman scattering (SFR) of the SRR by excited electrons,
4. SFR of the laser by excited electrons and its interaction with the SRR.

From the observed shift of the band gap by exchange and correlation energy the number of created electron-hole pairs can be calculated to be up to 10¹⁶ per cm³. The observed acceptor binding energy varies from 66 cm^?1 atB=0 to 71 cm^?1 at 4.5T.     

Electrodynamics of rotating planetary plasmaspheres in a dipole magnetic field

As a model of the actual structure of the planetary plasmasphere, we consider the electrodynamical problem of electric field and current generation by a planet with a dipole magnetic field corotating with the plasma envelope. The plasma envelope is characterized by the conductivity and angular velocity of the magnetospheric plasma as functions of the distance τ from the planet center and the angle ? measured from the rotation axis. The exact solutions of the Maxwell equations are obtained in the axially symmetric case within the framework of unipole electrodynamics when the rotational and magnetic axes coincide. These solutions describe the possible distributions of electric fields, currents, and charges in the rotating plasma envelope surrounding the magnetized planet. As an exmple, we constructed, using the theory proposed, the exact solution corresponding to the following structure of the plasmasphere:

1. the plasmasphere region corotating with the planet and located between L-shells (L=τ/Rsin ² ?, where R is the radius of the planet) from L=1 to L=L_*;
2. the polar region with differential, spherically symmetric rotation;
3. the transient region of the plasmasphere rotating differentially with the angular velocity dependent on the L-number and located between L-shells from L=L_* to L=L_*+L₀;
4. the external (vacuum) region.

Analysis of the multipole expansion of the electrostatic potential showed that the electric field potential is equal to zero in the external region (L>L_*+L₀), independently of the number of the boundary L-shell. This solution can serve as a basis for simulation of the plasmasphere formation processes, taking into account the actual conditions in the near-planetary plasma envelopes.