Structure,phase composition,and spectral luminescence properties of partially stabilized zirconium dioxide crystals doped with Yb<Superscript>3+</Superscript> ions

Investigation of partially stabilized zirconium dioxide crystals via transmission electron microscopy has revealed a developed twin structure therein. The following compositions of the above crystals have been selected for this study: 97.2 mol % ZrO₂–1.0 mol % Y₂O₃–1.8 mol % Yb₂O₃; 97.2 mol % ZrO₂–2.0 mol % Y₂O₃–0.8 mol % Yb₂O₃; 97.2 mol % ZrO₂–2.5 mol % Y₂O₃–0.3 mol % Yb₂O₃; and 96.3 mol % ZrO₂–3.4 mol % Y₂O₃–0.3 mol % Yb₂O₃. X-ray diffraction analysis of these crystals indicate the presence of transformable (t) and nontransformable (t') tetragonal phases. Optical spectroscopy measurements of ZrO₂–Y₂O₃–Yb₂O₃ crystals with tetragonal and cubic structures have highlighted in Yb³⁺-doped zirconium dioxide samples the formation of the optical centers of the Yb³⁺ ions is observed, whose crystal surrounding is similar to those in cubic zirconium dioxide crystals.     

Effect of iso- and heterovalent additives on characteristics of highly transparent Nd(Yb):Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The possibility of synthesis and characteristics of highly transparent Y₂O₃ ceramics doped with Nd³⁺ and Yb³⁺ were studied. The ceramics crystal structure was disordered for the first time by simultaneously substituting Y³⁺ cations by Lu³⁺ or Sc³⁺ isovalent ions and Zr⁴⁺ heterovalent ions. The developed technique allowed synthesis of highly transparent Nd³⁺:Y₂O₃, Nd³⁺: Y₂O₃ + 6 mol % ZrO₂, Nd³⁺: (Lu_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂, Nd³⁺:(Sc_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂, and Yb³⁺:(Sc_0.25Y_0.75)₂O₃ + 6 mol % ZrO₂ ceramics with transmittance to 82.2%. It was shown that introduction of iso- and heterovalent additives Sc₂O₃, Lu₂O₃, and ZrO₂ into Nd³⁺:Y₂O₃ decreases average crystallite sizes to ∼1 μm and reduces the pore content, thus making it possible to produce pore-free ceramics. These additives broaden the spectral band of the ⁴ F _3/2 → ⁴ I _11/2 transition of the neodymium ion to 40 nm.     

Structure and spectral-luminescence properties of yttrium-stabilized zirconia crystals activated with Tm<Superscript>3+</Superscript> ions

Yttrium-stabilized zirconia crystals (ZrO₂-13.8 mol % Y₂O₃-0.2 mol % Tm₂O₃ and ZrO₂-12 mol % Y₂O₃-2 mol % Tm₂O₃) have been grown by directed crystallization from a melt in a cold container using direct high-frequency melting. The crystals have been analyzed by X-ray diffraction. The spectral-luminescence properties have been studied, and the cross-relaxation efficiency for Tm³⁺ ions (³ H ₄ → ³ F ₄, ³ H ₆ → ³ F ₄) in these crystals has been estimated.     

The effect of prestressing on the fracture toughness of ZrO2-(3, 4) mol % Y2O3 ceramics

It is shown that the fracture toughness of prestressed ZrO₂-(3, 4) mol % Y₂O₃ ceramics monotonically increases, the growth being as high as ∼50% of the initial value. It is believed that prestressing causes slow isothermal martensite transformation of some grains in the material. During mechanical tests, the degree of transformation rises, which shows up as increased fracture roughness.     

Effect of the loading rate on the mechanical properties of polycrystalline samples of a ZrO2-3 mol. % Y2O3 solid solution

The dependence of the bending strength and fracture toughness of polycrystalline samples of a solid solution of ZrO₂-3 mol. % Y₂O₃ on the traverse rate of a test machine has been studied in the velocity interval of 0.005–50 mm/min. It is shown that the strength and the fracture toughness are virtually constant in the interval of loading rates of 0.05–5 mm/min. An increase of the loading rate to 50 mm/min is accompanied by a significant decrease (by a factor of 2 or 3) in both the strength and the fracture toughness. When the loading rate is decreased to 0.005 mm/min, a slight increase (10–15%) in the fracture toughness and a comparable decrease in the strength is observed. An experiment has also been done to see how the mechanical properties measured at a loading rate of 0.5 mm/min are affected by holding polycrystalline samples of a solid solution of ZrO₂-3 mol. % Y₂O₃ under load for several hours. Holding the samples under a load causes a significant increase (by 30–50%) in both the strength and the fracture toughness. The observed phenomena are explained in terms of the variation of the amount of Y₂O₃, which stabilizes the metastable tetragonal phase of a solid solution of ZrO₂. Fiz. Tverd. Tela (St. Petersburg) 39, 880–884 (May 1997)     

Influence of yttrium on EPR characteristics of chromium ions in nanoscale particles of zirconium dioxide

The EPR and proton magnetic resonance methods were applied to study zirconium hydroxide samples which transformed to nanoscale ZrO₂ powders upon annealing. The samples were obtained from solutions with mixture compositions (ZrO₂ + 0.5 mol % Cr₂O₃) and (ZrO₂ + 3 mol % Y₂O₃ + 0.5 mol % Cr₂O₃). The influence of yttrium on the recharging of the chromium ion upon annealing of samples was studied in the temperature range 100–950°C. A significant influence of yttrium on internal stresses caused by heating and cooling in the lattice of nanoscale ZrO₂ particles was detected using the EPR method. It was shown that the typical features of the influence of yttrium on total (over the entire crystallite) and local (near chromium ions) lattice distortions depend on the sample heating temperature and are different for various annealing temperatures.     

Intrinsic luminescence centers in scandia,yttria, and their solid solutions

Pulsed cathodoluminescence (PCL) of Y₂O₃ and Sc₂O₃ powders, as well as of ceramic samples of binary (11 mol % Sc₂O₃–ZrO₂ and 10 mol % Y₂O₃–ZrO₂) and ternary (xSc₂O₃–(10–x)Y₂O₃–ZrO₂) (x = 5, 6, 7, 8 mol %) solid solutions are studied in the range of 300–850 nm at room temperature. In Y₂O₃ and Sc₂O₃, series of strong narrow luminescence bands emitted by surface bound radicals _...0^...0>-Y=O and _...0^...0>-Sc=O are found. The PCL spectra of xSc₂O₃–(10–x)Y₂O₃–ZrO₂ ceramic samples showed the same series of narrow bands at 543, 551, 555, 572, 583, 594, 614, and 639 nm as the yttrium oxide spectra. The existence of these luminescence bands, which correspond to the emission of the _...0^...0>-Y=O radical, and the absence of the emission lines of the _...0^...0>-Sc=O radical indicate that yttrium ions, due to their larger radius, are the first that are displaced to the surface of crystallites in these systems, which is accompanied by the formation of the second phase in subsurface layers.     

Mechanoelectric effect in solid electrolytes

The mechanoelectric effect in solid electrolytes of the compositions ZrO₂ + 8 mol % Sc₂O₃ and ZrO₂ + 8 mol % Y₂O₃ is investigated experimentally. The mechanical properties of polycrystalline specimens are studied using four-point bending in air. It is shown that a negative charge is induced on the extended side of the bent specimen and that the magnitude of this charge depends on the external mechanical load and the temperature of measurement. The assumption is made that the observed phenomena are associated with the uphill diffusion of vacancies in response to a nonuniform field of mechanical stresses. The theoretical model is compared with the experimental results.     

Optical and structural properties of thin films deposited from laser fused Zirconia,Hafnia, and Yttria

The optical and structural properties of films deposited from laser sintered Zirconia (ZrO₂), Hafnia (HfO₂), and Yttria (Y₂O₃) and from the commercially available (unprocessed material) Zirconia, Hafnia and Yttria, were studied and compared. All the films had low absorption. Films deposited from the laser sintered material had very low optical inhomogeneity. ZrO₂ films showed negative inhomogeneity for films deposited from the unprocessed material. The refractive index increased for ZrO₂ films deposited from the laser sintered material. HfO₂ and Y₂O₃ films showed positive inhomogeneity when deposited from the unprocessed material. The refractive index of the films of these materials decreased when deposited from the laser sintered material. The thin films of ZrO₂ and Y₂O₃ prepared from laser sintered material had stable monoclinic and cubic structures respectively while HfO₂ films were found to be amorphous.     

Development of ceria-doped zirconia electrolytes with high toughness and ionic conductivity

Development of Y₂O₃ stabilized ZrO₂ electrolytes for solid oxide fuel cell with better mechanical properties was attempted. 3 mol% Y₂O₃ stabilized ZrO₂ doped with 3–15 mol% CeO₂ was investigated in the present work. The results reveal that the toughness and the bending strength of 3–6 mol% CeO₂ doped 3 mol% Y₂O₃–ZrO₂ are much higher than that of 8 mol% Y₂O₃–ZrO₂. The best ionic conductivity observed in 6 mol% ceria-doped 3 mol% Y₂O₃–ZrO₂ electrolyte is better than that of 8 mol% Y₂O₃–ZrO₂ at 800 °C, which indicates the possibility of developing ZrO₂-based electrolyte with enhanced toughness.     

Y2O3 stabilized ZrO2 thin films deposited by electron beam evaporation: Structural, morphological characterization and laser induced damage threshold

Four kinds of Y₂O₃ stabilized ZrO₂ (YSZ) thin films with different Y₂O₃ content have been prepared on BK7 substrates by electron-beam evaporation method. Structural properties and surface morphology of thin films were investigated by X-ray diffraction (XRD) spectra and scanning probe microscope. Laser induced damage threshold (LIDT) was determined. It was found that crystalline phase and microstructure of YSZ thin films was dependent on Y₂O₃ molar content. YSZ thin films changed from monoclinic phase to high temperature phase (tetragonal and cubic) with the increase of Y₂O₃ content. The LIDT of stabilized thin film is more than that of unstabilized thin films. The reason is that ZrO₂ material undergoes phase transition during the course of e-beam evaporation resulting in more numbers of defects compared to that of YSZ thin films. These defects act as absorptive center and the original breakdown points.     

Highly transparent ceramics with disordered crystal structure

A highly transparent ceramic has been synthesized from Nd³⁺:Y₂O₃ to which 6 mol. % ZrO₂ and 25 mol. % Sc₂O₃ or Lu₂O₃ were added for disordering the crystal structure. Nanopowders with an average particle size of 10–15 nm served as an initial material. They were compacted by the method of uniaxial static pressing combined with ultrasonic action on nanoparticles. The compacting pressure was 200 MPa; the power of the ultrasonic generator was 1.5 kW. It has been shown that the replacement of Y by isovalent Sc and Lu ions and by heterovalent Zr ions reduces the content of pores and the sizes of crystallites. The transparency of the Nd³⁺:Y₂O₃ ceramic with these additives reaches a maximum of 82.2%, and the 40% intensity level spectral band corresponding to the ⁴F_3/2 → ⁴I_11/2 transition widens from 11.4 to 40 nm.     

Transport characteristics of phonons and the specific heat of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:ZrO<Subscript>2</Subscript> solid solution single crystals

The temperature dependences of the specific heat and transport characteristics of phonons in single crystals of yttrium-stabilized zirconium dioxide Y₂O₃:ZrO₂ solid solutions have been studied. It has been shown that the temperature dependences of the specific heat at T > 5 K are almost identical at the degree of stabilization of a solid solution with an Y₂O₃ content of 5–20 mol %. Differences in the temperature dependences of the specific heat of samples from different sources at T < 5 K are due to the presence of low-energy two-level systems. The features of the transport characteristics of thermal phonons at liquid helium temperatures reflect not only the presence of two-level systems but also the scattering of phonons on low-dimensional domains of another phase coherently conjugate to the main phase of the Y₂O₃:ZrO₂ solid solution.     

Y2O3·Cr2O3复合氧化物热力学性质的研究

在1182—1386K温度范围内,用固体电解质氧浓差电池:Mo|Cr,Y₂O₃,Y₂O₃·Cr₂O₃|ZrO₂(+MgO)|Cr,Cr₂O₃|Mo测定了复合氧化物Y₂O₃·Cr₂O₃的热力学性质。对于反应Y_{2关键词：}     

Synthesis of Y2Si2O7:Eu nanocrystal and its optical properties

Nanocrystalline Y₂Si₂O₇:Eu phosphor with an average size about 60 nm is easily prepared using silica aerogel as raw material under ultrasonic irradiation and annealing temperature at 300-600 °C and this nanocrystalline decomposes into Y₂O₃:Eu and silica by heat treatment at 700-900 °C. The excitation broad band centered at 283 and 254 nm results from Eu³⁺ substituting for Y³⁺ in Y₂Si₂O₇ and Y₂O₃/SiO₂, respectively. Compared with Y₂O₃:Eu/SiO₂ crystalline, the PL excitation and emission peaks of Y₂Si₂O₇:Eu nanocrystalline red-shift and lead to the enhance of its luminescence intensity due to the different chemical surroundings of Eu³⁺ in above nanocrystallines. The decrease of PL intensity may be ascribed to quenching effect resulting from more defects in Y₂O₃:Eu/SiO₂ crystalline.     

Enhanced optical activation of Er in Er-doped Al2O3 powders by Y codoping in a sol-gel method

Enhanced photoluminescence (PL) mechanism of Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping at wavelength 1.53 μm has been investigated through PL measurements of 0.1 mol% Er³⁺- and 0-20 mol% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900 °C in a non-aqueous sol-gel method. PL intensity and lifetime of Er³⁺-Y³⁺-codoped Al₂O₃ powders composed of γ-(Al,Er,Y)₂O₃ and θ-(Al,Er,Y)₂O₃ phases increased with increasing Y³⁺-codoping concentration. The 10-20 mol% Y³⁺ codoping in 0.1 mol% Er³⁺-doped Al₂O₃ powders intensified the PL intensity by about 20 times, with a PL lifetime prolonged from 3.5 to 5.8 ms. A maximal increase of the optical activity of Er³⁺ in 0.1 mol% Er³⁺-Y³⁺-codoped Al₂O₃ powders about one order was achieved by 10-20 mol% Y³⁺ codoping. It is found that the improved PL properties for Er³⁺-Y³⁺-codoped Al₂O₃ powders are mainly attributed to enhanced optical activation of Er³⁺ in the Al₂O₃ by Y³⁺ codoping, and to the slightly increased radiative quantum efficiency of Er³⁺ in the Al₂O₃.     

Conductivity of Fe2O3-doped YSZ

Effect of 2 mol.% Fe₂O₃ addition on conductivity of yttria stabilized zirconia ceramics (YSZ, 6–12 mol.% Y₂O₃) was established. For Fe doped material, it was shown that conductivity demonstrates maximum at 10 mol.% Y₂O₃, and its value increases by 1.4 times. Conductivity maximum corresponds with the minimal volume of crystal lattice. Discussion of results was performed in terms of the model that assumes the control effect of hydrostatic pressure on oxygen ions diffusion.     

Impedance spectroscopy analysis of percolation in (yttria-stabilized zirconia)-yttria ceramic composites

(ZrO₂:8 mol% Y₂O₃)+m mol% Y₂O₃ ceramic composites with nominal yttria concentration varying from 0 to70 mol% (0–82.9 vol.%) were prepared by evaporation of a suspension of ZrO₂:8 mol% Y₂O₃ and Y₂O₃ in ethanol followed by pressing and sintering. The samples were analyzed by X-ray diffractometry and scanning electron microscopy for microstructural characterization. The electrical properties were studied by impedance spectroscopy (IS) allowing for the separation of the inter- and intragranular components of the electrical conductivity. The percolative behavior of these components was analyzed using the general effective media (GEM) equation and the percolation thresholds found were ∼28 vol.%. The results indicate that impedance spectroscopy provides useful information in addition to the dc techniques concerning the electrical characterization of composite materials.     

The effect of flux materials on the physical and optical properties of Eu-activated yttrium oxide phosphors

A flux fusion method was used to obtain the various sizes of Eu³⁺-activated Y₂O₃ red phosphors. The flux material was selected as an independent variable to control the physical properties of phosphor particles and their effects on the morphology and size distribution of phosphors were examined by scanning electron microscopy. The concentration of the flux materials and synthetic temperature were optimized for maximal photoluminescence intensity. Fluoride-based flux materials were found to work for the crystal formation of Eu³⁺-activated Y₂O₃. In particular, when a BaF₂ flux was used during the reaction at 1450 °C for 3 h, the photoluminescence (PL) intensity of Eu³⁺-activated Y₂O₃ was 25% higher than that without a flux and spherical phosphors had a mean particle size of 4-5 μm. The morphology and size distribution of the synthesized Eu³⁺-activated Y₂O₃ phosphor were predominantly dependent upon the type and concentration of flux material and synthetic temperature.     

Electrodeposition and characterization of Ni-Y2O3 composite

Nano-sized Y₂O₃ particles were codeposited with nickel by electrolytic plating from a nickel sulfate bath. The effects of the incorporated Y₂O₃ on the structure, morphology and mechanical properties (including microhardness, friction coefficient and wear resistant) of Ni-Y₂O₃ composite coatings were studied. It is observed that the addition of nano-sized Y₂O₃ particles shows apparent influence on the reduction potential and pH of the electrolyte. The incorporated Y₂O₃ increases from 1.56 wt.% to 4.4 wt.% by increasing the Y₂O₃ concentration in the plating bath from 20 to 80 g/l. XRD results reveal that the incorporated Y₂O₃ particles favour the crystal faces (2 0 0) and (2 2 0). SEM and AFM images demonstrate that the addition of Y₂O₃ particles causes a smooth and compact surface. The present study also shows that the codeposited Y₂O₃ particles in deposits decrease the friction coefficient and simultaneously reduce the wear weight loss. Ni-Y₂O₃ composite coatings reach their best microhardness and tribological properties at Y₂O₃ content 4.4 wt.% under the experiment conditions.