M. Hartmanová

Characterization of yttria-stabilized zirconia thin films deposited by electron beam evaporation on silicon substrates

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ–Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y2O3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ–Si interface and hence the accessible sweep of the surface potential. The capacitance–voltage characteristics of the metal–insulator–semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages.

Correlation between microscopic and macroscopic properties of yttria stabilized zirconia: 1. Single crystals

Abstract This paper reports on the results of the research on the yttria-stabilized zirconia single crystals and on the defects obtained in the wide range of yttria amounts, 1.13 x

Dielectric properties of ceria and yttria-stabilized zirconia thin films grown on silicon substrates

Abstract The dielectric permittivities of fcc yttria-stabilized zirconia (YSZ) and ceria (CeO 2 ) thin films as-grown on n-doped Si(100) substrates by electron beam evaporation at 200°C in the metal–insulator–semiconductor (MIS) configuration have been investigated. Two independent methods were used for this purpose, the high frequency limiting capacitance C P and feedback charge C – V plots. The values obtained are 16.8 (YSZ) and 2.8 (CeO 2 ) in the case of C P and 18.3 (YSZ) and 3.4 (CeO 2 ) from the C – V measurements. The hysteresis of C – V curves observed for both Al/YSZ and CeO 2 /Si/Au structures can be ascribed to the slow redistribution of negative mobile charges (oxygen ions O 2− ) present inside the YSZ and CeO 2 films.

Influence of copper- and iron-doping on cubic yttria-stabilized zirconia

Cubic yttria-stabilized zirconias (YSZs) (15 mol% Y2O3) doped with 2 wt% CuO and 0.3 wt% Fe2O3, respectively, have been compared with undoped YSZ. The lattice constants were found to increase in the sequence:aYSZ <aYSZ/Fe <aYSZ/cu. Vickers microhardness of polycrystalline YSZ/Fe exceeds that of polycrystalline YSZ/Cu, whereas the hardness of the single crystalline materials YSZ/Fe and YSZ/Cu are nearly identical and consistently lower than the polycrystalline values. Raman and infrared spectra reveal a breakdown of the selection rules, i.e. these techniques probe the local, non-cubic arrangement of oxygen vacancies. The findings are discussed in terms of a substitutional versus an interstitial-doping model.

Structure and electrical conductivity of multicomponent metal oxides having scheelite structure

The investigated bismuth vanadate, BiVO4, bismuth vanadomolybdate, Bi0.85V0.55Mo0.45O4, and pure bismuth molybdate, Bi2Mo3O12, oxides prepared by novel spray drying technique having the scheelite structure were found to be monoclinic in the case of BiVO4 and Bi2Mo3O12, whereas Bi0.85V0.55Mo0.45O4 is body-centered tetragonal. The distribution of intergranular porosity across polycrystalline samples is inhomogeneous, being larger parallel to the flat compression of the powder samples. The high polarizability of Bi3+ cations with their lone-pair electrons influences stability of the disordered oxygen sublattice. All as-prepared systems undergo a slight structural change of the oxygen arrangement during the sample heating in the temperature region of 340–390°C, probably due to an order ⇆ disorder transition, resulting in a decrease of lattice oxygen ion mobility and decrease of electrical conductivity. The total bulk electrical conductivity of both vanadate systems is essentially ionic at low temperatures and high oxygen partial pressures. Diffusion of the lattice oxygen ions in the Bi1−x/3V1−xMoxO4 scheelite structure is indirectly related to the introduction of cation vacancies. The highest conductivity was observed in the multicomponent oxide Bi0.85V0.55Mo0.45O4, both as-prepared and thermally treated. Above 350°C the conductivity of BiVO4 and partially also Bi0.85V0.55Mo0.45O4 oxides is affected by the n-type electron contribution.

Preparation and properties of transparent thoria-yttria ceramics

Abstract Precipitation and sintering conditions of thoria-yttria have been optimized to obtain transparent ceramics at low sintering temperatures. Density, micro- and X-ray structure, electrical conductivity and light transmission of the sintered bodies have been determined.

Electrical behaviour of HfO2 stabilized with rare earths

Abstract The investigation of the electrical characteristics of monocrystalline HfO 2 +15 mol% Ln 2 O 3 (Ln=Sc, Ub, Y, Tb, Gd, Er) has shown: (a) the Sc 2 O 3 was found to be the most suitable stabilizer for HfO 2 ; (b) the electrical conductivity of this system is one order of magnitude higher in comparison with the other used oxides, the conductivities of which are very similar; (c) the temperature dependence of conductivities has an Arrhenius character with the activation energies form 1.10 eV to 1.38 eV; (d) the behaviour of the relative permittivity, ϵ r , in the investigated systems, has a similar character as their conductivity.

Structural and electrical properties of double-layer ceria/yttria stabilized zirconia deposited on silicon substrate

Abstract Analyses of the phase composition and electrical characterization of double-layer CeO 2 /YSZ and single-layer CeO 2 , YSZ dielectrics grown on a Si (100) substrate at 200°C by electron beam evaporation as well as of the quality of interfaces between the oxide layers and silicon substrates were performed. The structure of all investigated oxide layers was found to be of the fcc fluorite type. The electrical conductivity of the investigated oxide layers and the average grain size change due to the post-deposition thermal treatment. The temperature dependence of the activation energy of the electrical conductivity is associated with different impurity phases in the oxide layers. Due to the lowest density of defects assessed from deep-level-transient-spectroscopy (DLTS) measurements, the CeO 2 /Si interface seems to be an optimum compared to the other oxide layer configurations. The dielectric constants e r (YSZ)=18.3 and e r (CeO 2 )=3.4 were estimated from the accumulation capacitances of the C – V curves.

The influence of tungsten on the oxygen sublattice in yttria-stabilized zirconia (YSZ)

Abstract The study of electrical conductivity, Raman and IR spectra, and microhardness of both polycrystalline and single crystalline forms of samples has proved that the kind of incorporation of tungsten into the YSZ lattice is a function of its concentration. However, the influence of tungsten impurity on the investigated physical properties of YSZ is rather weak. The electrical conductivity does not change markedly its character with an exception of an anomaly at 0.1–0.2 wt% WO 3 . The observed decrease of the intensities of the defect-induced Raman bands can be caused by the strong electronic influence of W 6+ ions on their environment and by the decrease of the number of oxygen vacancies in the structure. The dependence of the microhardness on the temperature is stepwise. The inhomogeneities observed are connected with different impurity phases. The microhardness is independent of the presence of tungsten above 375 °C, which indicates the absence of tungsten containing impurity phases at these temperatures.

Structure and physical properties of stabilized HfO2-R2O3 (R = Sc, Yb, Y, Tb, Gd, Er)

Abstract The structure, Raman and IR reflectance spectra and electrical conductivity of 85 mol% HfO2 + 15 mol% R2O3 (R = Sc, Yb, Y, Tb, Gd, Er) single crystals have been investigated. It was found that: 1. (1) HfO2-R2O3 (R = Sc, Yb, Y, Tb, Gd, Er) are substitutional cubic solid solutions; HfO2-Sc2O3 is either a metastable cubic or stable rhombohedral substitutional arrangement; 2. (2) the observed IR-active phonons and defect-induced Raman spectra are related to the structural differences between HfO2-R2O3 solid solutions, i.e., for R = Yb, Y, Tb, Gd, Er the symmetry is Oh5 and for HfO2-Sc2O3 the symmetry is D37; Kramers-Kronig analysis gave the resonant frequencies ωTO and ωLO; 3. (3) for all dopants investigated the electrical conductivity decreased as the dopant radius increased. The activation energy for conduction was found to increase with increasing dopant ionic radius. The fact that the highest electrical conductivity among 15 mol% R2O3 doped systems was obtained with HfO2 + Sc2O3 suggests that deformation of the coordination polyhedron around cations and the radius ratio r d r h play important roles in determining the electrical conductivity behaviour.