Yttria-stabilized Zirconia Single Crystals Research Articles

Carrier concentration dependence of optical and magnetic properties in epitaxial manganese-doped indium tin oxide films with different manganese concentrations

Epitaxial manganese-doped indium tin oxide (Mn-doped ITO) films with different Mn concentrations were deposited on single-crystal yttria-stabilized zirconia substrates using radio-frequency magnetron sputtering. The carrier concentration of the epitaxial Mn-doped ITO films could be controlled by changing the Mn doping concentration. The optical bandgaps of the films increased with the increase in the carrier concentration. Room-temperature ferromagnetism was observed in all films irrespective of the Mn concentration. The saturation magnetizations of the films increased with the increase in the carrier concentration, which suggests that delocalized charge carrier-mediated interaction model is one of the most probable mechanisms of the ferromagnetism in the Mn-doped ITO films. We found that the carrier concentration plays a crucial role in controlling optical and magnetic properties of the Mn-doped ITO films. The results of this study provide useful insight into the application of Mn-doped ITO films to ferromagnetic electrodes in spintronic devices.

Optical properties of yttria-stabilized zirconia from spectroscopic ellipsometry

Complex dielectric function (ɛ = ɛ1 + iɛ2) spectra of a heat treated single crystal yttria-stabilized zirconia (YSZ) have been determined over a spectral range of 0.03–8.5 eV using spectroscopic ellipsometry. Spectra are collected using three instruments covering different parts of the measured spectrum. The YSZ sample is modeled as a semi-infinite bulk crystal covered by a surface layer described by a Bruggeman effective medium approximation of equal parts YSZ and void.

Up-Conversion Photoluminescence in Thulia and Ytterbia Co-Doped Yttria-Stabilized Zirconia Single Crystals

ZrO2 is an attractive host matrix for luminescence material because of its excellent physical properties, such as low phonon energy and wide band gap. In this work, the highly transparent Tm2O3 and Yb2O3 co-doped yttria stabilized zirconia (YSZ) (abbreviated as Yb/Tm: YSZ) single crystals were grown by the optical floating zone method. The Yb/Tm: YSZ samples were stabilized in the cubic phase at room temperature when Yb3+ and Tm3+ replaced Y3+. The influence of Yb3+ co-doping on the up-conversion luminescence properties of the crystals was systematically studied. A total of 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3 co-activated YSZ single crystal (abbreviated as 2.0Yb/Tm: YSZ) has the maximum luminous intensity. There were seven absorption peaks located at around 358, 460, 679, 783.3, 850–1000, 1200, and 1721.5 nm that were observed in the absorption spectrum of the 2.0Yb/Tm: YSZ single crystal. There were three up-conversion peaks at around 488, 658 and 800 nm that were observed when the Yb/Tm: YSZ samples were excitated at 980 nm. The fluorescence lifetime of Tm3+ for the 1G4→3H6 transition of the 2.0Yb/Tm: YSZ sample is 7.716 ms as excited with a 980 nm laser. In addition, the oscillator strength parameters Ωλ (λ = 2, 4 and 6) of this sample were derived by the Judd–Ofelt theory to evaluate the laser performance of the host materials. The ratio Ω4/Ω6 of this sample is 0.80, implying its excellent laser output. Therefore, the 2.0Yb/Tm: YSZ single crystal is a considerable potential material for laser and luminescence applications.

White light luminescence in Dy/Tm co-doped yttria stabilized zirconia single crystals

A series of high quality Dy2O3 and Tm2O3 co-doped yttria stabilized zirconia (YSZ) single crystals was synthesized. These crystals have a single cubic structure, and exhibit the characteristic of Dy3+ (blue and yellow emissions) and Tm3+ (blue emission) under excitation with NUV light. Importantly, the hue can be varied between blue and white by modifying the Tm3+/Dy3+ ratio. The photoluminescence and decay curves are consistent with the existence of resonance-type energy transfer from Tm3+ to Dy3+ ions via an electric multipole interaction mechanism. Maximum luminescence intensity is observed in YSZ doped with 0.50 mol% Tm2O3 and 0.75 mol% Dy2O3, and this sample has CIE coordinates (x = 0.33, y = 0.33) in accordance with those for white chromaticity. Thus, the outstanding luminescence properties of these single crystals suggest potential applications in white light emission devices.

Ferromagnetism in defective yttria-stabilized zirconia

Significant research attention has been devoted to identifying and synthesizing new magnetic materials via doping of non-magnetic materials. The material defects offer an approach to stabilize ferromagnetism in non-magnetic materials such as oxygen-deficient HfO2 and oxygen-deficient ZrO2. In this study, we demonstrated room-temperature ferromagnetism via nitrogen ion implantation on yttria-stabilized zirconia (YSZ) single crystals. The results of structural and chemical analyses indicate the formation of a distinct surface layer through the implantation of nitrogen ions and potential oxygen vacancies. The lattice constant in this surface layer increased by 0.6% compared to the bulk value. Nitrogen ions were observed in this region, and their concentration was estimated to be 2.32 atoms per unit cell. In contrast to the lack of magnetic hysteresis in a YSZ single crystal, ferromagnetic hysteresis was observed in the ion-implanted YSZ crystals, owing to defects—nitrogen ions and oxygen vacancies in the surface layer.

Femtosecond Laser-Induced Anisotropic Structure and Nonlinear Optical Response of Yttria-Stabilized Zirconia Single Crystals with Different Planes.

Nonlinear optical properties have been extensively studied due to their promising nonlinear effects and various applications. With ultrashort duration and ultrahigh intensity, a femtosecond laser can fabricate various superior-quality micro-/nanostructures to improve the nonlinearity of materials, which are promising for stable and high-performance nonlinear devices. In this contribution, yttria-stabilized zirconia (YSZ) with fs laser-induced micro-/nanostructures is demonstrated to exhibit unique anisotropic light-material interaction and nonlinear optical response on [100], [110], and [111] planes. Time-resolved reflectivity of YSZ after fs laser excitation is investigated by a pump-probe experiment, which is consistent with simulations through the plasma model combined with a two-temperature model. These results indicate two early ablation mechanisms: Coulomb explosion and melting. Anisotropic crack structures are formed due to thermal stress, which is always ignored in fs laser fabrication and is verified by Raman mapping and analysis of slip systems on different crystal planes. Through the z-scan measurement, the nonlinear absorption (NLA) of crack structures is effectively improved, and a nearly 18 times enhancement of the NLA coefficient is acquired in [100] samples, while a 2 times enhancement in [110] and [111] samples. Such great enhancement of NLA is mainly due to the abundant presence of crack structures and the increase of fs laser-induced oxygen vacancies in [100] YSZ. These results provide a potential way of utilizing fs laser to improve the nonlinearity for the technological development in nonlinear devices.

Microstructural modifications induced in Si+-implanted yttria-stabilised zirconia: a combined RBS-C, XRD and Raman investigation.

The structural differences in (100)-, (110)- and (111)-oriented cubic yttria-stabilised zirconia (YSZ) single crystals after implantation with 2 MeV Si+ ions at the fluences of 5 × 1015, 1 × 1016 and 5 × 1016 cm-2 were studied using Rutherford backscattering spectrometry in the channelling mode (RBS-C), X-ray diffraction (XRD) and Raman spectroscopy. The RBS-C results show that the damage accumulation in the 〈110〉 direction exhibits a lower level of disorder (<0.3) than the other orientations (<0.6) and it seems that the (110) crystallographic orientation is the most resistant to radiation damage. The experimental results from the RBS measurement were compared with the results from the XRD measurements. The XRD data were analysed using the standard two-beam dynamical X-ray diffraction theory and the pure isotropic strain was deduced from the fit for the fluence of 5 × 1015 cm-2. It was shown that the maximum value of the isotropic strain does not depend on the surface orientation. The increase in signal intensity at ∼689 cm-1 is probably related to an increase in implantation defects such as oxygen vacancies.

Upconversion Visible Light Emission in Yb/Pr Co-Doped Yttria-Stabilized Zirconia (YSZ) Single Crystals

As a development on previous research on single crystals of Pr3+-doped yttria-stabilized zirconia (YSZ), we report here the preparation and optical properties of Yb/Pr co-doped YSZ single crystals with different Yb2O3 concentrations. Results from X-ray diffraction (XRD) and Raman spectroscopy indicated that all of the crystal samples had a cubic phase structure, and transmission was ≥88% in the 550–780 nm range. Photoluminescence (PL) under excitation with a 980 nm laser showed upconversion emission, and several peaks were observed centered on 448 nm, 508 nm, 525 nm, 542 nm, 617 nm and 656 nm. The effects of excited state absorption (ESA), energy transfer upconversion (ETU), cross relaxation (CR), and cooperative energy transfer (CET) on the upconversion luminescence and energy transition mechanism in YSZ crystals were further studied. The fluorescence lifetime of the 3P0 → 3H5 transition at 542 nm reached 207 μs, which shows that the samples are of potential use for laser and fluorescence output.

Nanoindentation of single-crystal and polycrystalline yttria-stabilized zirconia: A comparative study by experiments and molecular dynamics simulations

A combination of nanoindentation experiments and molecular dynamics (MD) nanoindentation simulations is carried out in this paper to study the mechanical properties and deformation behaviors of single-crystal and polycrystalline yttria-stabilized zirconia (YSZ). Different Young’s moduli are found in the nanoindentation experiments of single-crystal and polycrystalline YSZ samples, though these two YSZ materials almost have the same hardness. In addition, with the aid of atomic force microscopy, different deformation behaviors are observed in single-crystal and polycrystalline YSZ. The different Young’s moduli and deformation behaviors of single-crystal and polycrystalline YSZ observed in experiments are explained by MD simulations. The simulation results show that during the indentation process, the slip occurs inside single-crystal YSZ but along the grain boundaries of polycrystalline YSZ. These different deformation mechanisms between single-crystal and polycrystalline YSZ account for the lager Young’s modulus and more significant pile-up phenomenon observed in single-crystal YSZ. In addition, our MD simulations also reveal that the mechanical properties of YSZ are almost independent of the temperature but can be significantly affected by the number of YSZ grains. Specifically, both the Young’s modulus and hardness of polycrystalline YSZ are found to decrease as the number of grains grows.

Crystal growth, structure and optical properties of Pr3+-doped yttria-stabilized zirconia single crystals* *Project supported by the National Natural Science Foundation of China (Grant No. 11975004) and the Key Research and Development Plan Project of Guangxi, China (Grant No. Guike AB18281007).

The development of blue semiconductor light-emitting diodes (LEDs) has produced potential applications for Pr-doped materials that can absorb blue light, especially crystals, and we now report structure and optical properties for high-quality Pr-doped single crystals of yttria-stabilized zirconia (YSZ) grown by the optical floating zone (FZ) method. X-ray diffraction (XRD) and Raman spectroscopy showed that all of the single crystal samples were in the cubic phase, whereas the corresponding ceramic samples contained a mixture of monoclinic and cubic phases. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy showed that Pr was present as the Pr3+ ion in ceramic rods and single crystals after heating to high temperatures. The absorption and photoluminescence excitation (PLE) spectra of the Pr-doped YSZ crystals measured at room temperature showed strong absorption of blue light, while their photoluminescence (PL) spectra showed five emission peaks at 565 nm, 588 nm, 614 nm, 638 nm, and 716 nm under 450 nm excitation. The optimum luminescence properties were obtained with the crystal prepared using 0.15 mol% Pr6O11, and those with higher concentrations showed evidence of quenching of the luminescence properties. In addition, the color purity of Pr-doped YSZ single crystal reached 98.9% in the orange–red region.

Localized electrochemical redox reactions in yttria-stabilized zirconia single crystals

Herein, electroreduction in yttria-stabilized zirconia are investigated by means of Hebb-Wagner polarization experiments. By performing optical and thermal microscopy on single crystals and thin films during the application of an electric field under vacuum or oxygen-tight sealed conditions, the movement of the reduction front from the cathode to the anode, which causes a blackening of the material, is monitored. When performing electrocoloration experiments on thin film samples, the progressing reaction of the blackened region was found to be inhomogeneous and evolves as a dendrite-like finger structure. The progression of the blackening fingers follow preferentially the electric field lines and thus are influenced by distortions in the field that can be caused by metallic particles embedded in the oxide. In contrast to this, in the first stage of the reduction process no significant influence of mechanically-induced dislocations on the morphology or kinetics on the electroreduction can be found. Only after a heavy electroreduction was a localized transformation of the surface region observed. There is an evolution of highly oxygen deficient ZrOx regions, which have a characteristic checked topography pattern at the microscale level.

Ion channelling effect and damage accumulation in yttria-stabilized zirconia implanted with Ag ions

Yttria stabilized zirconia (YSZ) is well known as a radiation-resistant material. In this study, we present results from 400 keV Ag+ implantations of the (1 0 0) YSZ single crystals to fluences ranging from 5 × 1015 to 5 × 1016 cm−2. The damage depth profiling and accumulation were probed using Rutherford backscattering spectrometry in the channelling mode (RBS-C), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The axial channelling effect of 2 MeV He+ ions in the implanted YSZ was studied. RBS-C provides us with detailed information about the displaced atoms density depth profiles progressing into greater depths, especially in the case of higher fluence. TEM was utilized to characterize the microstructure evolution and damage accumulation in the buried layer after the implantation. At the highest fluence (5 × 1016 cm−2), Ag depth profile in the depth of 30–130 nm was identified in TEM bright and dark field images as well as in the electron diffraction patterns. Ag depth profiles are in agreement with depth profiles determined by RBS which show maximum Ag concentration in the depth of 94 nm. The reason for the decrease of the deformation identified by XRD in the vertical direction is the defect formation.

Mechanical properties of Ar-ion irradiated single-crystals of YSZ grown in different crystallographic orientations

The influence of Ar+ ion irradiation on structural and nanomechanical properties of Yttria Stabilized Zirconia (YSZ) single crystals were studied. Specimens grown in three crystallographic orientations 〈1 0 0〉, 〈1 0 0〉 and 〈1 1 1〉 were irradiated at room temperature with 160 keV Ar-ions up to 3 fluences: 1 × 1014, 1 × 1015 and 1 × 1016 cm−2. Structural properties of the modified layers were measured by means of Grazing Incidence X-ray Diffraction (GI XRD) and Raman Spectroscopy techniques, whereas nanomechanical properties were asessed by using nanoindentation technique. Obtained results revealed shifts of the characteristic peaks and hardening effect in the function of Ar-ion fluence. Reported changes originate from at least two phenomena: (i) creation of radiation defects and (ii) local increase of stress induced by damage created by incoming ions – which magnitude may depend on crystallographic orientation.

Outstanding Oxygen Reduction Kinetics of La0.6Sr0.4FeO3−δ Surfaces Decorated with Platinum Nanoparticles

La0.6Sr0.4FeO3−δ (LSF64) thin films are prepared by pulsed laser deposition (PLD) on yttria stabilized zirconia single crystals (YSZ) and characterized by electrochemical impedance spectroscopy (EIS) measurements before and after decoration with platinum nanoparticles. The platinum on the surface of LSF64 strongly accelerates the oxygen surface exchange kinetics. Especially at low oxygen partial pressures, the area-specific resistance (ASR) decreases by almost two orders of magnitude (e.g. in 0.25 mbar pO2 from 125 Ωcm2 to ca. 2 Ωcm2 at 600 °C). While the pure LSF64 films exhibit severe degradation of the polarization resistance, Pt decorated films degrade much slower and show less scatter between individual samples. Surprisingly, faster oxygen incorporation (=lower polarization resistance) results for lower oxygen partial pressures, which indicates a severe mechanism change compared to undecorated LSF64 surfaces. The obtained results thus also reveal valuable information on the rate-determining step of oxygen exchange on LSF64 surfaces with and without platinum. On undecorated LSF64 surfaces oxygen dissociation is suggested to be rate limiting, while the Pt particles on LSF64 enable fast oxygen dissociation. Consequently, on Pt-decorated LSF64 electrodes a kind of job sharing mechanism results, with oxygen dissociation taking place on Pt and oxide ion formation and incorporation proceeding on the oxide.

Preparation and up-conversion luminescence of Er-doped yttria stabilized zirconia single crystals

High-quality yttria-stabilized zirconia (YSZ) single crystals doped with different concentrations of Er2O3 were grown by the optical floating zone method. The cubic phase of ZrO2 was retained when Er3+ partially replaced Y3+ in the YSZ matrix. Up-conversion luminescence was observed when the crystals were excited by a 980 nm laser diode. The optical power curve was obtained by plotting the up-conversion luminescence intensity against the laser power, and both the green and red light up-conversion were shown to involve two photons. Seven characteristic visible and three infrared absorption peaks were observed in the absorption spectrum of the 1.50 mol% Er2O3: YSZ. The up-conversion spectra produced three prominent peaks at 547(green), 561 (green) and 679 (red) nm. Green and red light maxima were observed with Er2O3 concentrations of 1.5 mol% and 0.5 mol%, respectively. Oscillator strength parameters Ωt (t = 2, 4, 6) were determined using the Judd-Ofelt theory and Ω2 = 9.90 × 10−20 cm2, Ω4 = 2.92 × 10−20 cm2, Ω6 = 3.32 × 10−20 cm2. The Ω4/Ω6 ratio (0.88), which is the key parameter for laser performance of reactive matrix materials, indicates that Er3+-doped YSZ has potential laser applications.

Growth and optical properties of thulia-doped cubic yttria stabilized zirconia single crystals

Abstract Single crystals of yttria stabilized zirconia (YSZ) doped with different thulia (Tm2O3) contents (0.2–3.0 mol%) (abbreviated to Tm2O3: YSZ) were grown by the optical floating zone method. The crystals were transparent and inclusion free. These samples were then analyzed by X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DSC), and Raman spectroscopy, and their optical properties were determined with Ultraviolet–visible (UV–Vis) and Photoluminescence spectroscopy (PL). The Tm2O3: YSZ single crystals were in the cubic phase, and the lattice parameters first increased and then decreased with increasing Tm2O3 content. The absorption spectra showed four peaks at around 356 nm (3H6→1D2), 460.5 nm (3H6→1G4), 678.5 nm (3H6→3F2,3) and 784 nm (3H6→3H4) in the visible region, and the optical bandgap energy increased with increasing Tm2O3 content, as a result of the Moss-Burstein effect. Measurements of PL spectra indicated a strong blue emission peak at 458 nm (1D2→3F4), and three weak emission peaks at 487 nm (1G4→3H6), 497 nm (1D2→3H5), and 656.5 nm (1G4→3F4) when the crystals were excited by light with a wavelength of 356 nm. The intensities of the emission peaks were strongly affected by the Tm2O3 content of the YSZ single crystals; the intensity increased with Tm2O3 content at low doping levels, reached the maximum at 0.5 mol% Tm2O3, then decreased with further increase in Tm2O3 content due to the concentration quenching effect. Additionally, the color changed from blue to cyan as the Tm2O3 content was increased. Overall, this work demonstrates that the cubic YSZ single crystal is a suitable host material for solid state luminescence.

Highly efficient up-conversion green emission in Ho/Yb co-doped yttria-stabilized zirconia single crystals

In the development of materials with valuable luminescence properties, we have used the optical floating zone method to prepare single crystals in the cubic phase of yttria-stabilized zirconia (YSZ) doped with 0.75 mol% Ho2O3 and various concentrations of Yb2O3. The influence of Yb3+ contents was determined for absorption and photoluminescence spectra, and fluorescence decay curves at room temperature. The absorption spectra consisted of several peaks that could be assigned to various transitions involving Yb3+ and Ho3+ ions, and oscillator strength parameters Ωt (t = 2, 4, 6) were determined using the Judd-Ofelt theory, along with the transition probability, lifetime, and branching ratio from the absorption and emission spectra of the crystal of YSZ co-doped with 0.75 mol% Ho2O3 and 1.5 mol% Yb2O3. The Ω2 value of ~14 × 10–20 cm2 indicates that the bonding around Ho3+ involves lower symmetry and higher covalency than in several other hosts, and the value of the ratio Ω4/Ω6 of 1.93 shows that this sample is a good candidate material for high quality laser output. Up-conversion emission spectra showed that Yb3+ doping significantly increased the emission intensity of 0.75 mol% Ho2O3 doped YSZ at green (557 nm), red (670 nm) and NIR (758 nm) wavelengths when excited by a 980 nm laser, and reached a maximum for 1.5 mol% Yb2O3. The emission at 557 nm was much sharper than that reported for nanocrystals of similar composition, where the maximum intensity was observed at 540 nm. Down-conversion PL spectra showed two prominent emission peaks at 1040 nm and 1213 nm, and the fluorescence decay curves indicate that energy transfer between Yb3+ and Ho3+ influenced the lifetime of the excited state of Ho3+ which varied with Yb2O3 concentration. Overall these results indicate that these Yb/Ho co-doped YSZ crystals have considerable potential for laser and luminescence applications.

Effect of the [formula omitted] tilt grain boundary on oxygen-ion movement in yttria-stabilized zirconia: Insights from molecular dynamics

We present a new methodology for investigating the combined effect of the Σ5(310)/[001] symmetric tilt grain boundary (GB) and the local cation environment in polycrystalline yttria stabilized zirconia (YSZ) on two important quantities that determine the ionic conductivity, namely, (i) the local hopping rate of O2− ion and (ii) the probability of O2--ion -vacancy pairs within the YSZ structure. How these quantities vary with distance to the GB core are estimated for the first time using waiting time distributions associated with O2− ion hop events in molecular dynamics simulations. We conclude that indeed fewer hop events occur in the presence of a GB. However, the GB effect can be felt at a far greater distance than previously believed. Most importantly, interactions between the O2− ions, nearby cations and the GB results in a hopping behavior that is different from one observed in single-crystal YSZ. Anisotropy in O2− ion movement in the vicinity of the GB is also studied. These results and the use of our novel technique have a direct implication on the development of improved models for ionic conduction in solid state electrolytes.

Preparation and optical properties of Ho3+-doped YSZ single crystals

Single crystals of yttria-stabilized zirconia (YSZ) doped with different contents of holmium were prepared by the optical floating zone method, and their structures and phase composition were characterized by XRD and Raman spectroscopy. These showed that the metastable tetragonal phase was stabilized by the substitutions. Transmittance of each of the Ho3+-doped YSZ single crystals was larger than 85% in the visible region. Measurements of fluorescence spectra indicated a strong emission at a wavelength of 553.5 nm, and two weak emission peaks at 671 nm and 759 nm when the crystals were excited by light with a wavelength of 448 nm. The YSZ doped with 0.75 mol% of Ho2O3 had a relatively higher fluorescence intensity and possessed high color purity (99.7%) in the green region, indicating that it can be used to produce efficient green emission.

Growth of epitaxial bismuth ruthenate pyrochlore films on yttria-stabilized zirconia (YSZ) and YSZ-buffered Si substrates by metal–organic chemical vapor deposition

Bismuth ruthenate (Bi2Ru2O7) thin films were deposited on (111) yttria-stabilized zirconia (YSZ) single crystals and (111)YSZ//(111)Si substrates by chemical vapor deposition using Bi(CH3)2[2-(CH3)2NCH2C6H4] and Ru(C7H11)(C7H9) as source materials and oxygen as a reactant gas. The film composition and X-ray diffraction ω-2θ scan profiles for thin films deposited using various source flow rate ratios revealed the existence of a process window to obtain stoichiometric Bi2Ru2O7. Within the process window, the kind of substrates did not strongly affect the deposition rates of Bi and Ru or the Bi/Ru ratio of the deposited films. It was also confirmed that the Bi2Ru2O7 thin films grew epitaxially on both substrates within the process window. In particular, epitaxial Bi2Ru2O7 thin films grew on the Si substrate with a YSZ buffer layer. Scanning electron microscopy revealed the formation of continuous dense Bi2Ru2O7 films without any cracks or voids, and a relatively smooth interface between Bi2Ru2O7 and the YSZ buffer layer on Si. The resistivity of the Bi2Ru2O7 films was almost constant (~550 and ~950 μΩcm for the films deposited on (111)YSZ single-crystal substrates and (111)YSZ//(111)Si substrates, respectively), even when the ratio of Bi and Ru source gas flow rates was changed in the process window. In addition, the resistivity of Bi2Ru2O7 films prepared on both kinds of substrates was almost independent of temperature from 10 to 300 K.