Dy2O3 Ceramics Research Articles

Fine-grained transparent Dy2O3 ceramics fabricated from precipitated powders without sintering aids

As a promising material for Faraday isolator used in visible and infrared range, Dy2O3 ceramics with the average grain size of ∼800 nm and the in-line transmittance of 79.3% at 2000 nm and 70.0% at 633 nm were successfully fabricated. The Dy2O3 wet-chemically precipitated powders were densified in two steps consisting of vacuum pre-sintering and hot isostatic pressing (HIP) post-treatment. The precipitated precursor was calcined at 1150–1250 °C for 4 h in air to obtain Dy2O3 powders. The influences of calcination temperature on the morphology and sintering behavior of Dy2O3 powders were studied. The optical quality and microstructure of Dy2O3 ceramics with different pre-sintering temperatures were investigated. The Verdet constant of Dy2O3 ceramics at 633 nm is −322.1 ± 3.5 rad T−1 m−1, about 2.4 times that of commercial Tb3Ga5O12 crystals. Transparent Dy2O3 ceramics with high Verdet constant and suitable transparent windows present a prospective application for Faraday rotators.

New optical ceramics: High-entropy sesquioxide X2O3 multi-wavelength emission phosphor transparent ceramics

Highly transparent X2O3 sesquioxide ceramics were obtained from a solid solution of five different oxides (Lu2O3, Y2O3, Yb2O3, Gd2O3, and Dy2O3), mixed in an equal molar ratio according to the principle of high-entropy. The fabricated (Lu, Y, Yb, Gd, Dy)2O3 ceramics achieved 99.97 % of the relative density and exhibited a high degree of optical transparency with the in-line transmittance of almost 80 % in the visible wavelength range. Emissions of Gd3+ (6PJ → 8S7/2 at 312 nm), Dy3+ (4F9/2 → 6H15/2 at 492 nm and 4F9/2 → 6H13/2 at 572 nm), and Yb3+ (2F5/2 → 2F7/2 at 1031 nm) suggested a potential application of the high-entropy ceramics as multi-wavelength emission phosphor transparent ceramics. High-entropy ceramics also exhibited lower specific heat and thermal conductivity compared to single-element sesquioxide ceramics. This work demonstrated that highly transparent oxide ceramics, with complex chemical compositions and good optical properties, could be obtained using the high-entropy principle.

Fabrication of Dy2O3 Transparent Ceramics by Vacuum Sintering Using Precipitated Powders

As a kind of promising material for a Faraday isolator used in the visible and near infrared range, Dy2O3 transparent ceramics were prepared by vacuum sintering from the nano-powders synthesized by the liquid precipitation method using ammonium hydrogen carbonate as precipitant with no sintering aids. The synthesized precursor was calcinated at 950 °C–1150 °C for 4 h in air. The influences of the calcination temperature on the morphologies and phase composition of Dy2O3 powders were characterized. It is found that the Dy2O3 powder calcinated at 1000 °C for 4 h is superior for the fabrication of Dy2O3 ceramics. The Dy2O3 transparent ceramic sample prepared by vacuum sintering at 1850 °C for 10 h, and subsequently with air annealing at 1400 °C for 10 h, from the 1000 °C-calcined Dy2O3 powders, presents the best optical quality. The values of in-line transmittance of the optimal ceramic specimen with the thickness of 1.0 mm are 75.3% at 2000 nm and 67.9% at 633 nm. The Verdet constant of Dy2O3 ceramics was measured to be −325.3 ± 1.9 rad/(T·m) at 633 nm, about 2.4 times larger than that of TGG (Tb3Ga5O12) single crystals.

Faraday Rotation of Dy2O3, CeF3 and Y3Fe5O12 at the Mid-Infrared Wavelengths

The relatively narrow choice of magneto-active materials that could be used to construct Faraday devices (such as rotators or isolators) for the mid-infrared wavelengths arguably represents a pressing issue that is currently limiting the development of the mid-infrared lasers. Furthermore, the knowledge of the magneto-optical properties of the yet-reported mid-infrared magneto-active materials is usually restricted to a single wavelength only. To address this issue, we have dedicated this work to a comprehensive investigation of the magneto-optical properties of both the emerging (DyO ceramics and CeF crystal) and established (YFeO crystal) mid-infrared magneto-active materials. A broadband radiation source was used in a combination with an advanced polarization-stepping method, enabling an in-depth analysis of the wavelength dependence of the investigated materials’ Faraday rotation. We were able to derive approximate models for the examined dependence, which, as we believe, may be conveniently used for designing the needed mid-infrared Faraday devices for lasers with the emission wavelengths in the 2- spectral region. In the case of YFeO crystal, the derived model may be used as a rough approximation of the material’s saturated Faraday rotation even beyond the 2- wavelengths.

Yttria nanopowders with low degree of aggregation by a spray precipitation method

Highly sinterable Y2O3 nano-powder with low degree of agglomeration was synthesized by using a spray precipitation technology, without the use of any additives and dispersants. Compared with the precursor made by using the dripping method (D-precursor), the precursor made by the spraying method (S-precursor) had much lower degree of hard agglomeration. So did the resultant calcined Y2O3 powder (S-Y2O3 powder) as compared with the D-Y2O3 powder. Sintering behaviors of the two powders were studied. Ceramics made from the S-Y2O3 powder (S-Y2O3 ceramics) showed much higher densification rate and final density. After vacuum sintered at 1650 °C for 5 h, relative density of the D-Y2O3 ceramics was merely 97.3%, while that of the S-Y2O3 ceramics reached 99.5%. In addition, the D-Y2O3 ceramics cannot be sintered to 98% relative density by using the vacuum sintering technique, due to the high degree of agglomeration of the D-Y2O3 powder. Moreover, the S-Y2O3 ceramic exhibited homogeneous microstructure and an in-line optical transmittance of 81.6% at 1200 nm after HIP treatment. The spray precipitation method should be applicable to synthesizing other oxide powders.

Enhanced piezoelectric properties in (Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 lead-free ceramics

(Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 ceramics (BCTSD-x, x = 0.02–0.10) were fabricated by conventional solid state sintering method. The effect of Ca2+ ions addition on the phase structure, microstructure, and electric properties of ceramics were studied. X-ray diffraction analysis reveals the replacement of Ba2+ ions in the perovskite structure by Ca2+ ions. Rhombohedral phase and tetragonal phase coexist in the composition with x = 0.06–0.10. Both d33 and Kp of the ceramics increase with increasing Ca concentration, and attain maximum values of 675 pC/N and 55.0%, respectively, for x = 0.06. All the ceramics present typical diffuse phase transition behavior, and the feature is not sensitive to the amount of Ca2+ ions.

Preparation and Performance of Neutron Absorbing Dysprosium Oxide Ceramic

Dysprosium is a kind of potential neutron absorption material with the thermal neutron absorption cross area of 950 Barn. In this paper, dysprosium oxide (Dy2O3) ceramic was prepared by pressureless sintering. The density, bending strength, fracture toughness and hardness of Dy2O3 ceramics under different sintering schedule were analyzed. The density of Dy2O3 ceramics was enhanced accompanied with the increase in sintering temperature, and it was close to the theoretical value when heated at 1630 °C. Bending strength reached a maximum of 117 MPa when sintering temperature was 1570 °C. However, fracture toughness was inversely proportional to the hardness approximately. As a consequence, the optimum sintering temperature for mechanical property of Dy2O3 ceramics was 1570 °C. The morphology of fracture surface was examined by SEM. The results showed that the porosity of Dy2O3 ceramics decreased with increasing temperature. Meanwhile, the Monte-Carlo software was used to simulate the neutron absorption property. The absorbtivity was about 99.13% when the neutron source was uniform energy spectrum of 10-11 Mev~10-5 Mev and the thickness of Dy2O3 was of 20 mm.

Dielectric and AC-conductivity studies of Dy2O3 doped (K0.5Na0.5)NbO3 ceramics

(K0.5Na0.5)NbO3 + x wt.% Dy2O3 (x = 0–1.5) ferroelectric ceramics were prepared by conventional solid state reaction method. XRD patterns revealed that orthorhombic symmetry has transformed into psuedocubic symmetry with increasing the substitution of Dy3+ in the Na+ site. Temperature and frequency dependences of relative dielectric permittivity maximum conforms the transformation from normal ferroelectric to relaxor ferroelectric behaviour. Frequency dependence of the relative dielectric permittivity maximum temperature observed for the samples with x ≥ 1.0 and satisfied the Vogel–Fulcher law. The diffuseness exponent γ (1.27–1.95) estimated from the high temperature slopes of the diffused dielectric permittivity data reveals that the degree of relaxor behavior increases with increasing the amount of Dy2O3. The temperature dependence of AC-conductivity σAC (T) analysis in the range 310 K < T < 470 K reveals the existence of variable range hopping of charge carriers with average hopping length RH and hopping energy EH are in the range 8.5–27 Å and 48–153 meV, respectively. Voltage dependent dielectric constant measurements confirm the ferroelectric nature of KNN+ x wt% Dy2O3 ceramics.

Dy2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 (BCTZ)+ xwt%Dy2O3(x = 0–0.20) ceramics were prepared by conventional solid-state process, and the effects of Dy2O3 on the microstructure and the electrical properties were investigated. X-ray diffraction pattern confirmed that the BCTZ ceramics exhibit tetragonal structure, and stable solid solutions between BCTZ and Dy2O3 were well established in the range investigated. SEM images show that the addition of Dy2O3 restrains abnormal grain growth and leads to the formation of homogeneous microstructures during sintering. Dy3+ occupies B-site at x = 0–0.15, and A-site at x = 0.20 respectively. A-site occupation of Dy3+ into BCZT ceramic facilitates the ferroelectric domains reorientation and thus improves the piezoelectric properties significantly from 315pC/N(x = 0) to 425pC/N(x = 0.20). The corresponding planar electromechanical coupling factor at x = 0.20 was 49.1%. The A-site occupation(x = 0.2) also exhibits superiority to the improvement of dielectric properties and ferroelectric properties for BCZT ceramics (ϵ33 = 3264 at 1 kHz, 2Pr = 28.4μC/cm2, 2Ec = 5.28 kV/cm).

Er2O3 Doping Effect on Varistor Properties and Multiimpulse Stress Behavior of ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 Ceramics

The Er2O3 doping effects on varistor properties and impulse aging behavior of the ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 ceramics were investigated in the range of 0–2.0 mol%. The nonlinear coefficient increased from 42 to 56 with an increase in the amount of Er2O3. The clamp voltage ratio (K) decreased with an increase in the amount of Er2O3. The varistors doped with 2.0 mol% in the amount of Er2O3 exhibited the best clamping characteristics, with K = 1.43–1.83 at an impulse current of 1–50 A. The varistors doped with 0.25 mol% in the amount of Er2O3 exhibited the strongest electrical stability, with the variation rate of the breakdown field of −0.5%, the variation rate of the nonlinear coefficient of −5.5%, and the variation rate of the leakage current of −1.5% after applying 400 times at an impulse current of 400 A

Major effects on varistor properties and impulse aging behavior of Zn–V–Mn–Co–Dy ceramics with small sintering changes

The effect of sintering temperature on varistor properties and impulse aging behavior of ZnO–V2O5–MnO2–CoO–Dy2O3 ceramics was systematically investigated. As the sintering temperature increased, the average grain size increased from 5.8 to 10.8 μm, whereas the sintered density decreased from 5.56 to 5.47 g/cm3. The breakdown field and the nonlinear coefficient increased from 1,812 to 3,379 V/cm and from 11 to 36, respectively, with an increase in the sintering temperature up to 925 °C. The varistor ceramics sintered at 950 °C exhibited the best clamp characteristics for the impulse-current of 1–50 A, with the clamp voltage ratio of K = 1.63–2.31. The varistor ceramics sintered at 925 °C exhibited the strongest stability against an impulse-current, with \( \% \,\Updelta {\text{E}}_{{ 1 {\text{ mA}}/{\text{cm}}^{2} }} = - 8. 1 \,\% ,\;\%\, \Updelta \alpha = - 4 4. 4\, \% ,{\text{ and}}\;\%\, \Updelta {\text{J}}_{\text{L}} = 3 8. 9\, \% \) after applying the multi-impulse-current of 400 A.