Quantification of local oxygen defects around Yttrium ions for yttria-doped ceria–zirconia ternary system

Local coordination structure around Yttrium ions in CeO₂–Y₂O₃ binary and [(CeO₂)_x(ZrO₂)_1?x]_0.8(YO_1.5)_0.2 (x = 0.0 ~ 1.0) ternary system has been investigated by ⁸⁹Y MAS-NMR. NMR spectra are found to be consisted of multiple peaks that can be assigned to 6-, 7- and 8-oxygen coordinated Yttrium ions. Compositional dependence of the spectrum was observed and compared with the previous results for ZrO₂–Y₂O₃ binary system. The present investigation suggested the degree of localization of the oxygen vacancy around the cation is in the order of Zr⁴⁺ > Y³⁺ > Ce⁴⁺. The degree of the oxygen vacancy preference for each cation was quantitatively determined for CeO₂–ZrO₂–Y₂O₃ ternary system the first time.     

+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

Defects in scandium doped barium zirconate studied by Sc-45 NMR

Local structure around Sc in BaZr_1 − xSc_xO_3 − δ protonic conductor has been investigated by ⁴⁵Sc MAS-NMR. The MAS-NMR spectra were consisted of several peaks, which can be assigned to Sc in different coordination environment. Compositional dependence of the spectrum was observed. The coordination environment of Sc is determined from the peak deconvolution, and the oxygen vacancy concentration and the protonic defect concentration around Sc were obtained. The present investigation suggests that oxygen vacancies preferentially located around Sc and the concentration of oxygen vacancies in the vicinity of Sc increases with increasing the Sc content. Protonic defects were found to be preferentially located around Sc at lower Sc content.     

Theoretical studies of the optical and EPR spectra for V in Y2O3 crystal

In this paper, we give an alternative suggestion that both the observed optical and electron paramagnetic resonance (EPR) spectra of Yttrium oxide (Y₂O₃):V³⁺ are attributed to V³⁺ ions at the S₆ site of Y₂O₃. This suggestion is different from the opinion in the previous paper that the optical and EPR spectra are attributed to V³⁺ ions at the C₂ and S₆ sites, respectively. From the suggestion, the optical band positions and spin-Hamiltonian parameters are calculated by diagonalizing the complete energy matrix for 3d² ions in trigonal symmetry. The results are in good agreement with the experimental values, suggesting that both the observed optical and EPR spectra in Y₂O₃:V³⁺ may be due to V³⁺ at S₆ site of Y₂O₃ crystal.     

Study on vacancy motion in Y2O3-doped CeO2 by 17O NMR technique

The ¹⁷O NMR measurement was made to elucidate the microscopic nature of vacancy motion in Y₂O₃-doped CeO₂. Spin-lattice relaxation rate, T^?1₁, spin-spin relaxation rate, T^?1₂, and resonance intensity were measured at v₀ = 8.13 MHz as a function of temperature [385 < T (K) < 1110] and composition [$\text{0.06 <}\text{Y}{}_2\text{O}{}_3\text{(}\text{m}\text{o}\text{) < 6}$]. The static electric field gradient associated with lattice defects resulted in the composition dependences of the line width and the intensity. In low dopant concentrations, doubly peaked temperature dependence of T^?1₁ was found, while a single and asymmetric peak was observed in high concentrations. T^?1₁ of 4.0 and 6.0 $\text{m}\text{o}$ doped samples were analyzed using a barrier height distribution model for the oxygen vacancy jump. The mean value of the activation energy was found to increase with the Y₂O₃ concentration.     

On the transferred hyperfine interaction in substituted yig

NMR of⁵⁷Fe is studied in a number of (M_xY_3–x) Fe₅O₁₂ garnets for small concentrations of M (M is either trivalent RE ion –Ho 3+, Gd 3+, Nd3+, Pr 3+, La 3+ or Bi 3+ ion). Beside the main resonance lines, the satellites were observed, which correspond to those Fe, in vicinity of which the impurity M is located. After correcting for the dipolar field, the field corresponding to the change of the transferred hyperfine interaction in M³⁺–O^2–-Fe³⁺ vs. Y³⁺–O^2–-Fe³⁺ triad was deduced from the satellites splitting. The analysis of the results indicates that the observed change in the transferred hyperfine field is mainly connected with the transfer of electrons between M³⁺ and Fe³⁺ ions and not with the local deformation around the impurity.     

89Yttrium nuclear magnetic resonance studies

With a Fourier-transform spectrometer, especially developed for nuclei with weak NMR signals, the lines of⁸⁹Y have been investigated in aqueous solutions of Y(NO₃)₃, YCl₃, and Y(ClO₄)₃. The concentration dependence of the chemical shifts of the⁸⁹Y resonance frequencies in these solutions were measured. Using this dependence, the Larmor frequency of the⁸⁹Y³⁺ ion solely surrounded by water was determined by extrapolation. The Larmor frequency of⁸⁹Y was referred to those of²H,³⁹K, and⁷³Ge with high accuracy. The magnetic moment of the⁸⁹Y³⁺ ion purely surrounded by H₂O molecules is μ(⁸⁹Y³⁺) = ?0.1368523(4) μ_N. The concentration dependence of Y(NO₃)₃ solutions in D₂O yields the solvent isotope effect δ(⁸⁹Y³⁺ in D₂O)?δ(⁸⁹Y³⁺ in H₂O)= ?(4.3±0.5)ppm. The⁸⁹Y relaxation times T₁ and T₂ of a 3 molal aqueous Y(NO₃)₃ solution were determined in the pH range ?0.5...+1.25. T₁ 190...90 s is nearly constant in this range, whereas the transverse relaxation rate T₂ ^?1 increases strongly with increasing pH; this effect seems to be due to the chemical exchange of the hydrated Y³⁺ ion between a monomer and a polymer site.     

Effect of substitutional order on the relaxation of aluminum nuclei in Y<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Lu<Subscript>x</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> mixed garnets

The spin-lattice relaxation time of ²⁷Al nuclei residing in the octahedral and tetrahedral oxygen environment in Y_{3 ?x}Lu_xAl₅O₁₂ mixed aluminum-yttrium garnets was measured by the NMR method for 0≤x≤3. A maximum in the concentration dependence of the relaxation time was observed for both crystallographic positions at x=0.75; this maximum correlates with the minimum in the NMR linewidth, indicating the ordering obtained as the yttrium and lutetium ions occupy the dodecahedral positions in the garnet lattice.     

A low temperature internal friction study of Y0.85Ca0.15Ba2Cu3O7−δ with different oxygen content

The ceramic sample of Y_0.85Ca_0.15Ba₂Cu₃O_7−δ was prepared by standard solid-state reaction method, and samples with different oxygen concentration were obtained by quenching from high temperature. The internal friction was measured using the vibrating reed method from liquid-nitrogen temperature to room temperature at kilohertz frequency. An internal friction peak was observed around 250 K in Y_0.85Ca_0.15Ba₂Cu₃O_7−δ quenched from 1023 K. The peak is related to the one observed around 220 K (labeled as P3 peak) in undoped YBa₂Cu₃O_7−δ (Y123). This result shows the dependence of P3 peak on carriers density and P3 peak has a strong correlation to the abnormal behavior of Y123 in the underdoped range. The variation of two low temperature thermal activated relaxation peaks (P1 and P2) on oxygen content were also investigated. And consistent explanations were given based on all recent researches.     

Boundary effects in finite Heisenberg antiferromagneticS = 1 chains:89Y NMR in Y2BaNi1−xMgxO5

By means of⁸⁹Y nuclear magnetic resonance (NMR) spectra direct evidence of staggered magnetization induced by a uniform field has been obtained in the Heisenberg antiferromagneticS = 1 chain Y₂BaNi_1?xMg_xO₅. A correspondence between the resonance lines and the lattice positions is established, providing an image of the alternating magnetic moments that develop around the Mg impurities at the chain boundaries. The amplitude of these moments is found to decrease exponentially from the edges, with a characteristic decay distance equal to the magnetic correlation length numerically evaluated for an infinite chain. While the magnetization pertaining to ions far from the boundaries behaves as in typical gapped systems, the edge spins exhibit anS = 1/2 Curie-like deviation. These results promote the NMR approach to access the spin-spin correlation function in antiferro-magnetic quantum spin systems at finite temperatures.     

Anelastic and dielectric relaxation of scandia-doped ceria

Of all the trivalent dopants which may be added to ceria (CeO₂) to make it an oxygen-ion conductor, Sc³⁺ appears to be unique in producing unusually low conductivity due to a relatively high vacancy-dopant association energy. In order to better understand the defect structure of Sc³⁺-doped ceria, the present work was undertaken using both anelastic and dielectric relaxation. A number of relaxation peaks were found. Most strikingly, a new low temperature relaxation with activation enthalpy near 0.2 eV was observed; it was shown to be due to a low-symmetry off-center configuration of an isolated Sć_Ce defect. At higher temperatures the relaxation due to Sc-V_o pairs (where v_o = oxygen vacancy) was found to have an activation enthalpy of 0.41 eV (much lower than that of larger dopant ions, e.g. Y³⁺ and Gd³⁺. In addition, complex relaxation spectra are observed even for concentrations as low as 0.3mol% Sc₂O₃, showing that higher clustered defects readily form in this system.     

Dielectric relaxation in YTTRIA-doped Ceria solid solutions

The nature of the defects present in Y₂O₃-doped CeO₂ is explored by means of dielectric relaxation, employing primarily the thermally-stimulated depolarization current (TSDC) technique. For Y₂O₃ concentrations ? 1 mole %, two relaxation peaks are observed. The lower-temperature peak shows a dielectric relaxation rate, τ^?1 which is $\text{1}\text{2}$ the relaxation rate of the corresponding anelastic relaxation. This proves that the peak is due to nn, 〈111〉 oriented, (YV_O) pairs, where V_O represents the oxygen vacancy. These pairs are positively charged defects which are compensated by an equal number of isolated Ý. The upper peak is a broad peak whose position varies with Y₂O₃ concentration in the same manner as the activation enthalpy for the ionic conductivity. The peak is not due to simple dipoles, but to relaxation of the array of alternately charged (YV_O) and Ý defects by the redistribution of oxygen-ion vacancies. A simple model, in which these defects form a superlattice containing wrong pairs, explains the essential features of the upper peak.     

Effect of Y2O3 addition on the conductivity and elastic modulus of (CeO2)1 − x(YO1.5)x

The conductivity and elastic modulus of (CeO₂)_1 − x(YO_1.5)_x for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y₂O₃; this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity, the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content of Y₂O₃ dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y₂O₃ dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y₂O₃, which also agreed with the experimental results. It was shown that the Y–O–Y bonding energy increased with the increasing content of Y₂O₃ dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y–O–Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y₂O₃ dopant content of approximately 20 mol%.     

Mössbauer study of cobalt ferrite nanocrystals substituted with rare-earth Y ions

Mössbauer spectroscopy is used to characterize the crystallite size and structure of CoFe_2−xY_xO₄ (x=0, 0.1, 0.3, 0.5) ferrite nanocrystallites synthesized by the sol-gel auto-combustion method. The effect of the substitution of Fe³⁺ ions by Y³⁺ ions on the structure of cobalt ferrite nanocrystallites is investigated. The Mössbauer spectra showed two sets of six-line hyperfine patterns for all the samples, indicating the presence of Fe in both A and B-sites. On increasing the concentration of doped Y, the hyperfine field strength and the isomer shift first increase and then decrease, whereas the quadrupole splitting continuously increases. The superparamagnetism was observed for all the samples and the change of ratio of the superparamagnetism component reflects the size of crystal grain.     

EPR investigation of local paramagnetic centers in perovskite-like crystals

In ScF₃ single crystals (pure and doped) as well as in Rb₂KScF₆ and Rb₂KDyF₆ crystals with a perovskite-like structure, point nanodefects (vacancy in place of trivalent cations) have been found and studied. Electron paramagnetic resonance has been used to investigate local paramagnetic centers that are not detected using X-ray diffraction. The angular dependence of the spectra indicates a local distortion of the cubic symmetry of the crystals. An additional hyperfine structure in the observed spectra is due to the delocalization of electrons over six F^? ions forming the first coordination polyhedron around the vacancy. The crystals studied are characterized by a high electron mobility and a high electron velocity, which depends on the impurity. The high mobility of electrons of the cation center can be indirectly responsible for the structural phase transition occurring in the ScF₃ crystal under uniaxial pressure.     

Effects of temperature and atmosphere on the magnetic properties of Co-doped ZnO rods

Co-doped ZnO (Zn_0.95Co_0.05O) rods are fabricated by co-precipitation method at different temperatures and atmospheres. X-ray diffraction, Energy dispersive X-ray spectroscopy and Raman results indicate that the samples were crystalline with wurtzite structure and no metallic Co or other secondary phases were found. Raman results indicate that the Co-doped ZnO powders annealed at different temperatures have different oxygen vacancy concentrations. The oxygen vacancies play an important role in the magnetic origin for diluted magnetic semiconductors. At low oxygen vacancy concentration, room temperature ferromagnetism is presented in Co-doped ZnO rods, and the ferromagnetism increases with the increment of oxygen vacancy concentration. But at very high oxygen vacancy concentration, large paramagnetic or antiferromagnetic effects are observed in Co-doped ZnO rods due to the ferromagnetic-antiferromagnetic competition. In addition, the sample annealed in Ar gas has better magnetic properties than that annealed in air, which indicates that O₂ plays an important role. Therefore, the ferromagnetism is affected by the amounts of structural defects, which depend sensitively on atmosphere and annealing temperature.     

Green luminescence and EPR studies on Mn-activated yttrium aluminum garnet phosphor

Yttrium aluminum garnet (Y₃Al₅O₁₂) and Mn activated Y₃Al₅O₁₂ phosphors have been prepared by urea combustion route in less than 5 min. The phosphors are well characterized by powder X-ray diffraction, Scanning electron microscopy and Fourier-transform infrared spectroscopic techniques. Photoluminescence tests on the pure Y₃Al₅O₁₂ showed a strong green emission at 525 nm (2.36 eV) attributed to the strongly allowed transition of F⁺ center whereas in Mn²⁺ activated YAG the green emission at 519 nm is due to the ⁴T₁ (G)→⁶A₁ (S) transition of Mn²⁺ ions. EPR studies have been carried out on Mn²⁺ activated Y₃Al₅O₁₂ phosphor at 300 and 110 K. From EPR spectra the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) indicates that the Mn²⁺ ions are in a moderately ionic environment. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.     

掺Gd3+,Y3+对PbWO_4低温热释光的影响

通过热释光方法研究了PbWO₄(PWO),PWO:Y³⁺,PWO:Gd³⁺多晶粉末及PWO,PWO:Y单晶的低温(<300K)热释光现象.多晶粉末中,掺杂Y³⁺或Gd³⁺都会大大降低甚至消除200K附近的热释光峰,同时产生新的热释光峰,分别位于125和150K(掺Y掺Gd).这表明掺三价离子除了起到电荷补偿作用以减少Pb³⁺,O^-浓度外,还可以产生新的陷阱能级.对于PWO:Y单晶,掺杂Y³⁺可以消除253K的热释光峰,即消除较深(～0.89eV)的陷阱,但PWO单晶中较浅的陷阱(～0.42eV)对应130K热释光峰仍然存在,对此进行讨论,它最可能源于氧空位缺陷.根据Pb³⁺,Gd³⁺,Y³⁺的电子库仑势不同,在PWO晶体中替代Pb²⁺后形成的电子陷阱深度有别(E_Pb>E_Gd>E_Y),从而解释了相应的热释光峰值温度的不同 关键词： 4')" href="#">PbWO₄ Y和Gd掺杂 热释光 陷阱     

Eu substitution and particle size control of Y2O2S for the excitation by UV light emitting diodes

Yttrium oxysulfide doped with europium (Y₂O₂S:Eu³⁺) red phosphor is used in UV light emitting diodes (LEDs) by mixing with blue and green phosphors to generate white light which are important for the application in general lighting. Here, we demonstrate the effect of shape and size and the concentration of activator (Eu) of red Y₂O₂S phosphor.