Impedance spectroscopy related to reversible water uptake and loss in polycrystalline Cu2+-stabilized K+-β″-ferrite

The conductivity and the reversible uptake and loss of water of a Cu²⁺-stabilized K⁺-β″-ferrite were investigated in a wet atmosphere between 20°C and 400°C by impedance spectroscopy and thermogravimetric analysis. Bulk, grain boundary and interface conductivities were separated and related to the structural water content as a function of temperature.     

Dielectric dispersion of ultrathin polymer Langmuir-Blodgett films

Dielectric dispersion is studied in films made of vinylidene fluoride/trifluoroethylene copolymer [P(VDF/TrFE)], which are obtained by the Langmuir-Blodgett technique in the temperature range from −90 to +132°C. The thickness of the films studied is ∼7 nm. A glass transition is observed in the temperature range from −40 to −50°C; this indicates the presence of an amorphous phase in the ultrathin Langmuir-Blodgett films.     

The effect of humidity on the ionic conductivity of Mg2+-stabilized K+-β-ferrite

The ionic conductivity of Mg²⁺-stabilized potassium β-ferrites was studied in wet and dry air atmosphere and in the temperature range between room temperature and 500 °C. Several conductivity processes were determined. The impedance spectroscopic measurements were combined with thermogravimetric analysis data, and a microscopic interpretation for the effect of humidity on the conductivity of K⁺-β-ferrite is proposed. Between 400 and 500 °C, a change in the conductivity behavior is observed which is associated with the magnetic ordering temperature and a structural ordering in the conductivity planes of the materials. The activation energy values of the different conduction processes have been calculated.     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

Growth of a textured quasicrystalline phase in Ti-Ni-Zr films prepared by pulsed laser deposition

The preparation in thin film form of the known icosahedral phase in Ti-Ni-Zr bulk alloys has been investigated as a function of substrate temperature. Films were deposited by pulsed laser deposition on sapphire substrates at temperatures ranging from room temperature to 350 °C. Morphological and structural modifications have been followed by grazing-incidence and θ–2θ X-ray diffraction, transmission electron diffraction and imaging. Chemical composition has been analyzed by electron probe microanalysis. The in-depth variation of composition has been studied by secondary neutral mass spectroscopy. We show that pulsed laser deposition at 275 °C makes the formation of a 1-μm-thick film of Ti-Ni-Zr quasicrystalline textured nanocrystallites possible. Received: 7 June 2001 / Accepted: 18 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +33-3/8357-6300, E-mail: brien@mines.u-nancy.fr     

Thermal transformations in soils studied by Mössbauer spectroscopy and x-ray diffraction

Mossbauer spectroscopy and X-ray diffraction techniques were used to investigate the iron oxides and other mineral phase developments in calcareous and noncalcareous soil samples after firing at ≈ 1000°C. Well crystalline haematite with larger particle size was produced in the fired non-calcareous soil. On the other hand, while goethite in the strongly calcareous natural material was transformed into haematite at the oven drying temperature, non of the latter was detected after firing at 1050°C. This could be related to the reaction between CaO, quartz and aluminosilicates at 800°C to produce calcium aluminosilicates which may have hindered the growth of haematite above this temperature.     

Charge/discharge characteristics of sulfur composite electrode at different temperature and current density in rechargeable lithium batteries

The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different current densities. The composite presented the discharge capacities of 854 and 632 mAh g⁻¹ at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g⁻¹ at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g⁻¹ at 55.6 and 667 mA g⁻¹, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g⁻¹.     

Photoluminescence,thermoluminescence and electron spin resonance studies on Eu<Superscript>3+</Superscript> doped Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript> red phosphors

Tricalcium aluminate doped with Eu³⁺ was prepared at furnace temperatures as low as 500°C by using the convenient combustion route and examined using powder X-ray diffraction, scanning electron microscope and photoluminescence techniques. A room-temperature photoluminescence study showed that the phosphors can be efficiently excited by UV/Visible region, emitting a red light with a peak wavelength of 616 nm corresponding to the ⁵D₀–⁷F₂ transition of Eu³⁺ ions. The phosphor exhibits three thermoluminescence (TL) peaks at 195°C, 325°C and 390°C. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the defect centres responsible for the TL process. Room-temperature ESR spectrum of irradiated phosphor appears to be a superposition of three distinct centres. One of the centres (centre I) with principal g-value 2.0130 is identified as O⁻ ion while centre II with an axially symmetric principal values g _∥=2.0030 and g _⊥=2.0072 is assigned to an F⁺ centre (singly ionized oxygen vacancy). O⁻ ion (hole centre) correlates with the TL peak at 195°C and the F⁺ centre (electron centre), which acts as a recombination centre, is also correlated to the 195°C TL peak. F⁺ centre further appears to be related to the high temperature peak at 390°C. Centre III is also assigned to an F⁺ centre and seems to be the recombination centre for the TL peak at 325°C.     

Growth of highly disordered InGaP on (100) GaAs by molecular beam epitaxy with a GaP decomposition source

High-quality, lattice-matched InGaP on exact (100) GaAs was successfully grown by molecular beam epitaxy with a GaP decomposition source. The ordering parameter (η) of the InGaP is investigated as a function of the growth temperature. η is as low as 0.22 and almost insensitive to the growth temperature below 460 °C. It increases abruptly around 475 °C and has a maximum value of 0.35 at ≈490 °C. Double crystal X-ray diffraction and a low-temperature photoluminescence spectrum reveal that the present growth method is robust and provides better quality InGaP compared to other state-of-the-art growth technologies. Received: 20 November 2000 / Accepted: 27 January 2001 / Published online: 21 March 2001     

Aluminum-assisted crystallization and <Emphasis Type="Italic">p</Emphasis>-type doping of polycrystalline Si

Aluminum-doped p-type polycrystalline silicon thin films have been synthesized on glass substrates using an aluminum target in a reactive SiH₄+Ar+H₂ gas mixture at a low substrate temperature of 300 °C through inductively coupled plasma-assisted RF magnetron sputtering. In this process, it is possible to simultaneously co-deposit Si–Al in one layer for crystallization of amorphous silicon, in contrast to the conventional techniques where alternating metal and amorphous Si layers are deposited. The effect of aluminum target power on the structural and electrical properties of polycrystalline Si films is analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and Hall-effect analysis. It is shown that at an aluminum target power of 100 W, the polycrystalline Si film features a high crystalline fraction of 91%, a vertically aligned columnar structure, a sheet resistance of 20.2 kΩ/□ and a hole concentration of 6.3×10¹⁸ cm⁻³. The underlying mechanism for achieving the semiconductor-quality polycrystalline silicon thin films at a low substrate temperature of 300 °C is proposed.     

Thermal effect on multiphonon-assisted anti-Stokes excited upconversion fluorescence emission in Yb3+-sensitized Er3+-doped optical fiber

The temperature effect upon infrared-to-visible frequency upconversion fluorescence emission in Yb³⁺-sensitized Er³⁺-doped germanosilicate optical fibers excited with cw radiation at 1.064 μm is investigated. The experimental results revealed an eightfold enhancement in the visible upconversion emission intensity as the fiber temperature was increased from 17 °C to 180 °C. The fluorescence emission enhancement is attributed to the temperature-dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium sensitizer. A theoretical approach that takes into account a sensitizer absorption cross-section, which depends on the phonon occupation number, has proven to agree very well with the experimental data Received: 6 April 1999 / Revised version: 27 August 1999 / Published online: 27 January 2000     

Instrumental complex and the results of precise measurements of millimeter- and submillimeter-wave propagation in condensed media and the atmosphere

We describe an instrumental complex based on high-Q open Fabry–Perot resonators for the frequency band 36–370 GHz and present original measurement techniques and the latest results of measuring (i) refractive indices and losses of modern high-quality dielectrics for high-power electronics (with prognosis for up to the terahertz band) and general-purpose dielectrics including films, (ii) reflectivities of both antenna reflectors of cryogenic-receiver radiotelescopes and the so-called “hot” antennas for future Mercurian missions, and (iii) the atmospheric absorption for the development of high-precision wave-propagation models including the continuum absorption. The instrumentation and the measurement techniques are intended for studying condensed-media parameters at temperatures 80–900 K and atmospheric parameters at temperatures from −40°C to +60°C and humidities from 0 to 80%.     

Study of field emission and dielectric properties of AlN films prepared by DC sputtering technique at different substrate temperatures

Nanocrystalline AlN thin films were prepared via DC sputtering technique at different substrate temperature. The crystal orientation and particle size of aluminum nitride thin films were investigated by XRD analysis. Study indicated that the sample contained pure phase hexagonal AlN nanoparticles with a single peak corresponding to the (100) planes. The peak at 665 cm⁻¹ in the FTIR spectrum of film was assigned to the LO phonon of hexagonal AlN. The particle size of the film, prepared at substrate temperature 200°C was about 9.5 nm, as investigated by atomic force microscope. Field emission study indicated that it can be used as a good field emitter. Turn-on field (E_to) of 15.02 V/μm was observed for the AlN films synthesized at substrate temperature 200°C. Dielectric constant of the AlN film was found nearly independent of frequencies in the measured frequency range 1 KHz to 1 MHz, i.e. in the audio frequency range. The values of dielectric constant (ε) were 10.07, 9.46 and 8.65 for the film prepared at 70°C, 150°C and 200°C, respectively, at frequency 1 KHz.     

Temperature dependence of microwave magnetic permeability spectra of Co0.7Zn1.3W hexaferrite nanopowders

The temperature dependence of complex magnetic permeability spectra of mechanically activated Co _0.7 Zn _1.3 W hexaferrite powders is investigated in the vicinity of the spin-reorientation transition in the frequency range from 0.2 to 11 GHz and temperature interval from −50 to +100 °C. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 35–39, September 2006.     

Structural and electrochemical characterization of Ce0.85Ca0.05Sm0.1O1.9 oxide ion electrolyte with Sr-doped LaMnO3 and SmCoO3 cathodes

This paper reports on the electrochemical properties and chemical stability of a recently developed Ca²⁺ and Sm³⁺-doped oxide ion conducting electrolyte, Ce_0.85Ca_0.05Sm_0.1O_1.9 (CCS), employed in an intermediate temperature solid oxide fuel cell (IT-SOFC) using conventional Sm_0.5Sr_0.5CoO₃ (SSC) and La_0.8Sr_0.2MnO₃ (LSM) cathodes in air at elevated temperatures. The materials were prepared by conventional solid-state reactions using their corresponding metal oxides and salts in the temperature range of 1,200–1,450 °C in air. Powder X-ray diffraction (PXRD) and impedance spectroscopy were employed for phase formation, chemical compatibility, and electrochemical characterization. PXRD studies on 1:1 weight ratio of heat-treated (1,000 °C for 3 days) mixtures of SSC or LSM and CCS revealed the presence of fluorite-type and perovskite-like phases. The area-specific resistance (ASR) value in air was lower for SSC cathodes (4.3–0.15 Ω cm²) compared to those of LSM (407–11 Ω cm²) over the investigated temperature range of 600–800 °C. As expected, a significant increase in ASR was observed in Ar as compared to air.     

Phase transition and copper ion conductor in PbBr2-CuBr

The solid solution of PbBr₂-CuBr has a high electric conductivity above 150 °C. The frequency and temperature dependences of complex dielectric constants have been investigated in the concentration of x=0.01-0.3. They exhibited a strong dieletric relaxation caused by the ionic conduction. Specific heat capacities have been measured in the temperature range from 100 to 200 °C. They showed no anomalous specific heat at the temperature 150 °C, but a distinct peak of heat was found at about 170 °C depending on the concentration. Using the simplified model of disorder of mobile ions, the excess specific heat was explained as the transition of copper ions between two sites. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Lattice thermal expansion of cesium plumbo chloride

The temperature variation of the lattice parameter of CsPbCl₃ in the cubic phase has been studied by x-ray method, from a determination of the precision lattice parameter at various temperatures, ranging from 50°C to 400°C. The coefficient of thermal expansion of CsPbCl₃ can be expressed by the quadratic equation,α _T = 21.6 × 10⁻⁶ + 2.44 × 10⁻⁹ T + 5.90 × 10⁻¹¹ T ².     

Effect of contacts between γ-Fe2O3 nanoparticles on their phase-transition temperature

The effect of mechanical contacts between γ-Fe₂O₃ particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential thermal analysis (DTA). The sample in which γ-Fe₂O₃ particles had no mechanical contacts with one another remained in the ferromagnetic state up to T _C = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C.     

Structural, electrical, and surface characteristics of La0.5Sr0.5CoO3 thin films prepared by pulsed-laser deposition

A parametric study of the growth of La_0.5Sr_0.5CoO₃ (LSCO) thin films on (100) MgO substrates by pulsed-laser deposition (PLD) is reported. Films are grown under a wide range of substrate temperature (450–800 °C), oxygen pressure (0.1–0.9 mbar), and incident laser fluence (0.8–2.6 J/cm²). The optimum ranges of temperature, oxygen pressure, and laser fluence to produce c-axis oriented films with smooth surface morphology and high metallic conductivity are identified. Films deposited at low temperature (500 °C) and post-annealed in situ at higher temperatures (600–800 °C) are also investigated with respect to their structure, surface morphology, and electrical conductivity. Received: 20 November 1998 / Accepted: 6 July 1999 / Published online: 21 October 1999     

Hydrothermally prepared oxide-ion and Mixed Conductors based on CeO2

The structure, thermal expansion coefficients, electrical and electrochemical properties of Ce_1−xM_xO_2−δ (M=Bi, La, Pr, Eu, Tb; x=0–0.30) solid solutions, prepared hydrothermally for the first time, are surveyed. For all cation substitution a solubility limit depending on the cation size was found. The uniformly small particle size (10–50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C, a significantly lower temperature, compared to that at 1600–1650 °C required for samples prepared by solid state techniques. X-ray absorption near edge spectroscopy (XANES) was used for the identification of Tb³⁺/Tb⁴⁺ or Pr³⁺/Pr⁴⁺ ions. The maximum of total conductivity in all solid solutions was found for x ∼ 0.15–0.25 with electronic contribution to the total conductivity ∼ 50 % for Tb/Pr substitution and close to zero in all other cases. The conductivity becomes more ionic with decreasing Tb/Pr substitution. The thermal expansion coefficients, determined from high-temperature X-ray diffraction data, are 11.7×10⁻⁶ K⁻¹ for CeO₂ and slowly decrease for Tb and increase for all other cases with increasing substitution. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.