H.A.M. van Hal

Processing and electrical properties of Pb (ZrxTi1−x)O3 (x=0.2–0.75) films: Comparison of metallo‐organic decomposition and sol‐gel processes

The deposition of thin Pb(ZrxTi1−x)O3 films by sol‐gel and by metallo‐organic decomposition (MOD) processes has been studied. Powders obtained from different precursor solutions were analyzed with respect to their decomposition and crystallization. Using a spin‐coating technique, Pb(ZrxTi1−x)O3 films with zirconium concentrations ranging from x=0.2 to 0.75 have been deposited on Pt‐electroded Si wafers. The lattice constants of the perovskite films and their dielectric and ferroelectric properties (permittivity, remanent polarization, coercive field strength) have been measured as a function of the zirconium concentration. The results are compared to the data obtained on bulk ceramics. For Pb(ZrxTi1−x)O3 films with a composition located at the morphotropic phase boundary (x≊0.53) the influence of the processing and the lead excess of the starting solutions on the film properties was examined. First measurements on the resistance degradation of thin Pb(Zr0.53Ti47)O3 films deposited by the MOD process are r...

Preparation and ferroelectric properties of PbZr0.53Ti0.47O3 thin films by spin coating and metalorganic decomposition

Films with a composition PbZr0.53Ti0.47O3 were prepared on different platinum bottom electrodes using a spin‐coating process followed by metalorganic decomposition. The film morphology and structure were characterized by scanning electron microscopy and x‐ray diffraction analysis. The morphology was strongly influenced by the heat cycle used to form the PbZr0.53Ti0.47O3 layer. Fast heating and high‐fire temperatures produced smooth films, while slow heating and low‐fire temperatures gave films having a rosette perovskite phase and an inter‐rosette second phase. The films were characterized electrically by measuring hysteresis loops and capacitance and conductance versus bias voltage and by pulse‐switching measurements. The dependence of the switched and nonswitched polarization on the number of switching cycles (i.e., the fatigue behavior) is found to be much better for fast‐heated than for slowly heated films. Switching lifetimes exceeding 1011 cycles were measured. The type of platinum bottom electrode ...

Properties of the tetragonal superconductor CaBaLaCu3Ox

Abstract The compound CaBaLaCu 3 O 6.9 is a tetragonal bulk superconductor with a T c of 80 K. CaBaLaCu 3 O x is isomorphic to tetragonal YBa 2 Cu 3 O x in which the Ca and La ions are both located at the Y- and Ba-site. High temperature X-ray diffraction and thermogravimetric measurements show no indication for “order-disorder” transitions involving the oxygen ions. TEM micrographs of CaBaLaCu 3 O x show no evidence for a / b twinning. The oxygen content and the partial oxygen pressure of CaBaLaCu 3 O x are determined as a function of temperature. The standard enthalpy change for the oxidation reaction, Δ H , is determined as 190.4(0.3) kJ⧸mol O 2 . Transmission electron diffraction patterns show weak but distinct half-order spots indicating an ordering which can be described by a supercell having axes twice as large as the basic unit cell.

Compounds in the system BaOY2O3

Abstract Starting with BaO and Y 2 O 3 , four compounds are found in the BaOY 2 O 3 system. At high temperatures (above 1200°C) two compounds mentioned in literature are found: Ba 3 Y 4 O 9 and BaY 2 O 4 . Heating the oxidic mixtures at 900°C results in the formation of a new compound Ba 2 Y 2 O 5 . This compound is transformed at 1000°C into another new compound: Ba 4 Y 2 O 7 . X-ray data of the four compounds are given in detail.

Materials with a high secondary-electron yield for use in plasma displays

Reduction of the firing voltage in plasma display panels calls for electrode coatings with a high secondary-electron yield. We have explored a range of materials that exhibit very low firing voltages, and a 50% reduction has been achieved relative to the best quality MgO. It is further shown that a high electron emission yield originates from both ion- and photon-induced processes, and is strongly influenced by the electronic structure of the material in terms of band gap and electron affinity.

Oxygen content, microstructure, and superconductivity of YBa2Cu3O7− x

The influence of preparation conditions and microstructure on the superconductive properties of single-phase poly-crystalline YBa 2 Cu 3 O 7− x was investigated by electron probe microanalysis, transmission electron microscopy (TEM), and x-ray powder diffraction as a function of temperature in various ambients supplemented by resistivity and susceptibility measurements. Leaching of Ba was observed when samples were brought in contact with water. The TEM imaging revealed that individual grains have an extremely defect-rich outer shell and an inner core with a domain structure with a and b axes interchanged. The transition temperature T c was found to decrease with increasing quench temperature in the range 400–900°C. The T c was observed to be linearly proportional to the difference in the orthorhombic cell parameters ( b-a ). Further implications are discussed.

Mechanochemical synthesis of BaTiO3, Bi0.5Na0.5TiO3 and Ba2NaNb5O15 dielectric ceramics

Abstract In the last years, mechanochemical alloying has been proven to be an important technology for the synthesis of intermetallic compounds. This technology has recently been used as a new route for the synthesis of inorganic compounds. The use of mechanochemical synthesis opens possibilities for the synthesis of complex systems at low temperatures. In this paper we discuss the preparation of the powders BaTiO3, Bi0.5Na0.5TiO3 and Ba2NaNb5O15 by mechanochemical synthesis. Phase formation is studied by X-ray powder diffraction. Since partly amorphous powders are obtained the crystallisation behaviour is further investigated by high temperature X-ray powder diffraction. Ceramic pellets have been sintered starting from as-milled powders as well as prefired powders. Microstructure and dielectric properties are characterised.

Hydrates of manganese (II) oxalate

Abstract In addition to the monoclinic ∝-dihydrate, it has now proved possible to prepare a second dihydrate, hitherto unknown. This compound, having an orthorhombic unit cell, proves to be the more stable modification of the dihydrates. For the trihydrate as well as for the anhydrous salt, orthorhombic unit cells were found. Prescriptions for the preparation of each of the hydrates are given. Some details are added about particle size, thermal decomposition and stability of the compounds, together with crystallographic and X-ray data.

The electrical and optical properties of thin layers of nano-sized antimony doped tinoxide particles

For the use in anti-static films on glass or polymeric substrates, transparent conductive layers can be prepared by spinning an aqueous suspension of nano-sized antimony-doped tinoxide (ATO) particles. These layers have a resistivity which is substantially higher than that of homogeneous ATO layers which are deposited by physical vapour deposition techniques. By curing the films to temperatures up to 700 °C, the resistivity of the particle layer can be decreased by two or three decades. Because the nano-sized particles are prepared by a low-temperature process a different mechanism can contribute to this decrease in resistivity. Possible effects which may influence the conductivity are sintering of the particles, change of the bulk material and the presence of an insulating layer at the outside of the particles. This decrease can be explained by the presence of an insulating antimony-rich layer on the outside of the particles, the thickness of which is reduced when the layer is cured. At temperatures above 350 °C, sintering of the particles also highly influences the decrease in resistivity. At temperatures above 700 °C, the resistivity is increased due to segregation of the antimony to the surface of the particle.

A 6Li, 7Li and 59Co MAS NMR study of rock salt type LixCoO2 (0.48≤x≤1.05)

Abstract Low temperature (LT, 400°C) and high temperature (HT, 900°C) Li x CoO 2 samples were synthesised with Li/Co ratios between 0.8 and 1.05. These samples were characterised by XRD, chemical analysis, 6 Li, 7 Li and 59 Co MAS NMR. 7 Li MAS NMR of the Li x CoO 2 -T 400 samples (LT) showed a single resonance line at −0.9 ppm, characteristic of lithium in an octahedral coordination. A somewhat narrower resonance at the same position was observed in the 7 Li MAS NMR spectra of the Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio ≤0.95. The Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio >0.95 showed several new lithium resonances, containing up to 35% of the signal intensity. The resonance positions of these new resonances indicate the presence of a paramagnetic cobalt species in the material. The 59 Co MAS NMR spectra of the Li x CoO 2 -T 900 samples revealed a spinning sideband manifold centred at ≈14 250 ppm for x ≤0.95 and three overlapping spinning sideband manifolds at ≈14 285, ≈14 260 and ≈14 230 ppm for Li/Co ratios >0.95. Compared to the Li x CoO 2 -T 900 samples the Li x CoO 2 -T 400 samples all showed one resonance with an increased line width. These resonance positions are typical for Co 3+ octahedrally coordinated by oxygen. No quadrupole induced shift is observed as a function of the external field (measurements performed at 14.1 and 7.05 T), indicating an undistorted octahedral coordination of cobalt in the materials studied. Chemical extraction of lithium with H 2 SO 4 leads to the formation of lithium that can not be detected with NMR. Electrochemical extraction of lithium, on the other hand, leads to a low field shift of the lithium resonance of 60–120 ppm, depending on the amount of lithium removed. Electrochemical intercalation (discharging) of the samples results in the reappearance of the original lithium spectra, showing the excellent reversibility of the charge/discharge process. Partly charged samples are characterised by signals in the range of 120–60 ppm and a signal at −0.9 ppm, indicating that part of the lithium remains in an unchanged environment. The dependence of the chemical shift on the amount of lithium removed is due to an rapid exchange process.