Hot-pressed Fe2+:ZnSe transparent ceramics with different doping concentrations

In this study, Fe²⁺:ZnSe transparent ceramics with different doping concentrations were prepared from annealed FeSe and ZnSe powders by hot pressing. The as-prepared ceramics consisted of a cubic ZnSe phase and compact microstructures. Doping concentrations of Fe²⁺ ions in the range 0.66–3.05 at.% were accurately realised, which could influence the absorption intensity of Fe²⁺:ZnSe transparent ceramics. An absorption peak was observed at ～3 μm, and its intensity could be controlled by the concentration of Fe²⁺ ions. Fe_xZn_1-xSe (0.0066 ≤ x ≤ 0.0305) ceramics with Fe²⁺ ions concentrations in the range 0.66–3.05 at.% exhibited significant absorption cross sections from 0.6676 × 10^?19 to 0.1075 × 10^?18 cm². The specimen doped with 1.55 at.% Fe²⁺ ions displayed the highest transmittance of 67% at a wavelength of 14 μm and a carbonate absorption peak at 9 μm. The proposed transparent ceramic technique appears promising for preparing Fe²⁺:ZnSe laser gain media because of its advantage of allowing control over Fe²⁺ concentration.     

Microstructure development and optical properties of Fe:ZnSe transparent ceramics sintered by spark plasma sintering

Fe:ZnSe transparent ceramics were prepared by spark plasma sintering. Fe:ZnSe powders synthesized via co-precipitation yielded well-dispersed particles with an average particle size of 550 nm. These powders were in the cubic phase Fe:ZnSe, indicating the successful substitution of Fe²⁺ for Zn²⁺. The highest relative density, 99.4%, was obtained by increasing the pressure and sintering time. The effects of sintering temperature, pressure, and time on the microstructure of SPS prepared ceramics were presented by micrographs. With increasing sintering temperature, from 600°C to 900°C, the average grain size increased from < 1 to 10 μm. The intergranular fracture indicated no neck formation in the sintering process. High pressure was essential for the densification process. The average grain size deceased from approximately 10 to 5 μm when the pressure was increased. Increasing the sintering time from 10 to 120 minutes lead to a change in the microstructure, from inter- to transgranular fracture, and eliminated the micropores. The as-prepared Fe:ZnSe ceramics were composed of single-phased cubic ZnSe. The sample sintered at 900°C under a pressure of 90 MPa for 120 minutes yielded a transmittance of approximately 60% at 1.4 μm and 68% at 7.5 μm and had residual micropores as its main scattering source. There was a strong characteristic absorption peak of Fe²⁺ ions at around 3 μm, which was red-shifted compared to Fe:ZnS transparent ceramics. Fe:ZnSe transparent ceramics have a reddish-brown color and it could be a promising mid-infrared laser material.     

Optical and Microwave Dielectric Properties of Zn‐Doped MgAl2O4 Transparent Ceramics Fabricated by Spark Plasma Sintering

(Mg_1?xZn_x)Al₂O₄ transparent ceramics were fabricated by spark plasma sintering technique at 1325°C for 10 min. A small mount of Zn²⁺ addition to MgAl₂O₄ ceramics was very effective to the performance improvement, while further increase in Zn‐doped content would give rise to the optical transmittance deterioration. The optical and microwave dielectric properties of MgAl₂O₄ transparent ceramics were improved by Zn substitution for Mg. The in‐line transmittance of the (Mg_1?xZn_x)Al₂O₄ (x = 0.02) ceramics can be as high as 70% at λ = 550 nm and 86.5% at λ = 2000 nm, respectively. The dielectric constant ε_r of (Mg_1?xZn_x)Al₂O₄ just varied from 8.32 to 8.54, however, the Q × f value increased significantly up to a maximal value of 66,000 GHz at x = 0.02. Moreover, the τ_f of (Mg_1?xZn_x)Al₂O₄ transparent ceramics changed from ?74 to ?65.5 ppm/°C. With the increasing of Zn‐doped content, the average grain size and the porosity increased, which was the primary reason for the change in optical and microwave dielectric properties.     

Fabrication and characterization of IR-transparent Fe2+ doped MgAl2O4 ceramics

Initial investigations on the preparation of highly transparent Fe²⁺:MgAl₂O₄ ceramics using nanopowders synthesized in a laser plume were carried out. For the first time, dense Fe²⁺:MgAl₂O₄ ceramics with high transmission in the mid-IR range were fabricated at a temperature as low as 1300°C and with a short sintering time (1 hour). The obtained Fe²⁺:MgAl₂O₄ ceramics contain a secondary (MgO)_0.91(FeO)_0.09 phase with a low wt% content, causing a substantial decrease in transmittance in the visible range. The transmittance increases with an increase in wavelength due to a decrease in Rayleigh scattering and reaches 85.6% at λ = 4 μm, which is close to the theoretical value. The absorption cross section of divalent iron ions was estimated to be σ = (1.66 ± 0.14) × 10⁻²⁰ cm².     

Synthesis and luminescence characterization of Pr3+, Gd3+ co-doped SrF2 transparent ceramics

Pr³⁺, Gd³⁺ co-doped SrF₂ transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF₂ transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF₂ (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr³⁺: ³P₀ → ³H₄ and ¹D₂ → ³H₄, respectively. With the co-doping of Gd³⁺ ions, the emission intensity of the Pr:SrF₂ transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF₂ transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr³⁺ doping concentrations, whereas the lifetimes decreased dramatically with the Pr³⁺ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF₂ transparent ceramic is a promising material for visible luminescent device applications.     

Microstructure and properties characterization of Yb:Lu2O3 transparent ceramics from co-precipitated nano-powders

5at.% Yb:Lu2O3 transparent ceramics were fabricated successfully by vacuum sintering along with hot isostatic pressing posttreatment from the nanopowders. The influences of calcination temperature on morphology and microstructures of powders and ceramics were studied systematically. The optimal ceramic sample from the nanopowder calcined at 1050°C shows uniform and dense microstructure with the in-line transmittance of 81.5% at 1100 nm. The results of the thermal measurements, that is, thermal conductivity and specific heat, were related to the changes occurring in the microstructure of the ceramics studied. It was shown on this basis that appropriate control of the technological process of sintering ceramics makes it possible to obtain laser ceramics with very good thermal properties as well as maintaining their high optical quality. Concerning the laser performance, the highest-optical quality 5at.% Yb:Lu₂O₃ sample was pumped in quasi-continuous wave conditions measuring a maximum output power of 2.59 W with a corresponding slope efficiency of 32.4%.     

Improved sinterability and microwave dielectric properties of [Zn0.5Ti0.5]3+-doped ZnAl2O4 spinel solid solution

Low-permittivity ZnAl_2-x(Zn_0.5Ti_0.5)_xO₄ ceramics were synthesized via conventional solid-state reaction method. A pure ZnAl₂O₄ solid-state solution with an Fd-3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn_0.5Ti_0.5]³⁺ for Al³⁺ effectively lowered the sintering temperature of the ZnAl₂O₄ ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (ε_r = 9.1, Q × f = 115,800 GHz and τ_f = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl₂O₄ ceramics.     

Microwave Sintering of Nanocrystalline Ni1−xZnxFe2O4 Ferrite Powder and Their Magnetic Properties

Nanocrystalline Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 1.0) powder with grain size of 30 nm was prepared using the spraying‐coprecipitation method. The obtained nanocrystalline Ni_1?xZn_xFe₂O₄ powder was sintered using conventional and microwave sintering techniques. The results show that the microstructure and magnetic properties of the sintered samples are obviously improved by microwave sintering of nanocrystalline Ni_1?xZn_xFe₂O₄ ferrite powder. The initial permeability of Ni_1?xZn_xFe₂O₄ ferrite increases with the increase in zinc concentration, although its resonance frequencies shift from high frequency to low frequency. The maximum initial permeability for microwave‐sintered Ni_0.4Zn_0.6Fe₂O₄ ceramic obtained at the temperature of 1170°C for 30 min reaches up to 360.9, and its resonance frequency is ~10 MHz. It may be attributed to the nanocrystalline Ni_1?xZn_xFe₂O₄ raw powder as well as the microwave sintering process, which results in a synergistic effect on improvement of the microstructure and magnetic properties.     

Highly transparent yttrium titanate (Y2Ti2O7) ceramics from co-precipitated powders

Highly transparent yttrium titanate (Y₂Ti₂O₇) ceramics were fabricated by vacuum sintering using co-precipitated powders for the first time. The effects of the powder calcination temperature on the phase composition, morphology of the calcined powders, and on the microstructure and transmittance of the Y₂Ti₂O₇ ceramics were investigated. When the calcination temperature was above 850 °C, pure phase Y₂Ti₂O₇ nanopowders with high sintering activity were obtained. Transparent Y₂Ti₂O₇ ceramics were obtained after vacuum sintered at 1600 °C for 6 h and annealed at 1100 °C for 5 h in air. The highest transmittance reached 73% at 1000 nm when the calcination temperature was 1150 °C. The measured refractive index of Y₂Ti₂O₇ ceramics was higher than 2.24 at the wavelength range of 350–1000 nm, making it a promising candidate for optical devices.     

Fabrication of 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 transparent ceramics by conventional sintering technique

0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ transparent ceramics were fabricated by a conventional sintering technique. Through optimization of sintering conditions of calcination and sintering temperatures and time, the obtained ceramics showed high optical transmittance of 53% and 71% at light wavelengths of 1300 and 2000 nm, respectively. The ceramics showed a rhombohedral to tetragonal phase transition at ~120°C and a tetragonal to cubic phase transition at 222°C. These transition temperatures were higher than those of 0.67Pb(Mg_1/3Nb_2/3)-0.33PbTiO₃ ceramics. In addition, the ceramics had a ferroelectric hysteresis loop, a large piezoelectric constant d₃₃ of 407 pC/N, and a planar electromechanical coupling factor k_p of 52%. These results suggest that the transparent ceramics may be used as a temperature-stable, linear electro-optic material.     

Fabrication and characterizations of Tb3Al5O12-based magneto-optical ceramics

Transparent terbium aluminum garnet (TAG)-based ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing (HIP) posttreatment from the co-precipitated TAG powders with different stoichiometric ratios. After component optimization, the transparent ceramics with TAG single-phase and attractive optical quality were obtained. The in-line transmittance of optimal Tb_(1+x)3(Al_0.996255Si_0.003745)₅O_{12.0093625+3x/2} (x = −.004, −.002) ceramics (1.7-mm thick) pre-sintered at 1700°C for 20 h with HIP posttreatment at 1700°C for 3 h under 176-MPa Ar reaches 82.6% at the wavelength of 1064 nm. With increasing terbium components, the secondary phase TAP appears in ceramics, which significantly degrades the optical quality of TAG-based ceramics. The Verdet constant of the TAG-based ceramics at 632.8 nm is about −181 rad T⁻¹ m⁻¹ at room temperature, which is about 33% higher than that of the TGG single crystals (−134 rad T⁻¹ m⁻¹).     

High-temperature BiFeO3–PbTiO3-Ba(Zr,Ti)O3 ternary ceramics with excellent piezoelectricity

Ternary ceramics of (0.87−x)BiFeO₃–xPbTiO₃–0.13Ba(Zr_0.5Ti_0.5)O₃ (BF–xPT–0.13BZT, 0.27 ≤ x ≤ 0.37) were prepared by the traditional solid state reaction methods. X-ray diffraction results display that BF-xPT-0.13BZT ternary ceramics of x ≥ 0.29 exhibit the perovskite structure with dominant tetragonal (T) phases mixed with a small amount of rhombohedral (R) phases. Scanning electron microscopy (SEM) images reveal that the average grain size of BF-xPT-0.13BZT ternary ceramics is in a range of 10–11 μm, increasing first and then decreasing with the increase of PbTiO₃ (PT) content. The low tanδ of about 0.015 and high Curie temperature T_c of above 450°C were obtained for BF-xPT-0.13BZT ternary ceramics. Moreover, the fluctuation of piezoelectric coefficient d₃₃ is less than ±10% over a broad temperature range of 30°C–400°C. BF-xPT-0.13BZT ternary ceramics for x = 0.33 possess the maximum T_c and d₃₃ of 470°C and 320 pC/N respectively, with the room temperature resistivity of about 10¹¹ Ω·cm. These results indicate that BF-xPT-0.13BZT ternary ceramics for x = 0.33 with both excellent piezoelectric properties and high Curie temperature have promising applications in high-temperature piezoelectric devices.     

A novel low-permittivity LiAl0.98(Zn0.5Si0.5)0.02O2-based microwave dielectric ceramics for LTCC application

Phase composition, morphology, and microwave dielectric properties of (1−x) LiAl_0.98(Zn_0.5Si_0.5)_0.02O₂ + x CaTiO₃ (0.05 ≤ x ≤ 0.20) materials synthesized via the solid state reaction method were investigated. All these densified materials were obtained at a sintering temperature of 1150°C. All compositions showed a major LiAlO₂ phase that was accompanied by a minor CaTiO₃ phase. The ε_r value increased gradually from 10.88 to 11.60, whereas the Q × f value remarkably decreased from 33 251 GHz to 13 511 GHz. The τ_f value changes from −85 ppm/°C to 212 ppm/°C, thereby indicating that CaTiO₃ could effectively adjust this value. HBO₃-doping was used to further decrease the sintering temperature to 900°C. The optimum value was obtained at 7 wt.% HBO₃ doped with microwave dielectric properties of ε_r = 9.39, Q × f = 10 224 GHz, and τ_f = −7.8 ppm/°C. This material also exhibited chemical compatibility with silver, making it a candidate for low temperature co-fired ceramics applications.     

Orthorhombic‐pseudocubic phase transition and piezoelectric properties of (Na0.5K0.5)(Nb1−xSbx)‐SrZrO3 ceramics

0.96(Na_0.5K_0.5)(Nb_1?xSb_x)‐0.04SrZrO₃ ceramics with 0.0≤x≤0.06 were well sintered at 1060°C for 6 hours without a secondary phase. Orthorhombic‐tetragonal transition temperature (T_O‐T) and Curie temperature (T_C) decreased with the addition of Sb₂O₅. The decrease in T_C was considerable compared to that in T_O‐T, and thus the tetragonal phase zone disappeared when x exceeded 0.03. Therefore, a broad peak for orthorhombic‐pseudocubic transition as opposed to that for orthorhombic‐tetragonal transition appeared at 115°C‐78.2°C for specimens with 0.04≤x≤0.06. An orthorhombic structure was observed for specimens with x≤0.03. However, the polymorphic phase boundary structure containing orthorhombic and pseudocubic structures was formed for the specimens 0.04≤x≤0.06. Furthermore, a specimen with x=0.055 exhibited a large piezoelectric strain constant of 325 pC/N, indicating that the coexistence of orthorhombic and pseudocubic structures could improve the piezoelectric properties of (Na_0.5K_0.5)NbO₃‐based lead‐free piezoelectric ceramics.     

Influence of inverse spinel structured CuGa2O4 on microwave dielectric properties of normal spinel ZnGa2O4 ceramics

Spinel Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics were prepared by the conventional solid‐state method. Only a single phase was indexed in all samples. The continuous lattice contraction of ZnGa₂O₄ unit cell was caused by Cu²⁺ substitution, and the lattice parameter shows a linear correlation with the content of Cu. The refined crystal structure parameters suggest that Cu²⁺ preferentially occupies the octahedron site, and the degree of inversion of Zn_1‐xCu_xGa₂O₄ (x = 0‐0.15) ceramics almost equals to the content of Cu²⁺. The relative intensity of A*_1g mode in Raman spectra confirm that the degree of inversion climbed with the growing content of Cu²⁺. The experimental and theoretical dielectric constant of Zn_1‐xCu_xGa₂O₄ ceramics fit well. Zn_1‐xCu_xGa₂O₄ (x = 0.01) ceramics sintered at 1400°C for 2 h exhibited good microwave dielectric properties, with ε_r = 9.88, Q × f = 131,445 GHz, tanδ = 6.85 × 10^?5, and τ_f = ?60 ppm/°C.     

Fabrication and properties of transparent Nd-doped BaF2 ceramics

Nd:BaF₂ nanoparticles have been prepared via co-precipitation and a pumping filtration wash method. The phase composition and morphology of the synthesized nanoparticles were investigated by X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM) analyses, respectively. SEM observations revealed the powder's particle size to be approximately 100-200 nm after calcination at 600°C for 5 hours in Ar. The transparent Nd:BaF₂ ceramics were then fabricated by the one-step vacuum sintering method at a temperature of 1200°C for 10 hours. SEM observations of the polished and thermally etched cross sections of the sintered ceramic revealed a highly homogenous microstructure with average grain size of 420 μm. Optical property characterization revealed that the transmittance of the ceramic reaches a maximum of ~70% in the infrared wavelength range, and an emission peak located at 1058 nm, excited by 808 nm light.     

Enhanced optical transmittance and energy-storage performance in NaNbO3-modified Bi0.5Na0.5TiO3 ceramics

Dielectric ceramics with both excellent energy storage and optical transmittance have attracted much attention in recent years. However, the transparent Pb-free energy-storage ceramics were rare reported. In this work, we prepared transparent relaxor ferroelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xNaNbO₃ (BNT–xNN) by conventional solid-state reaction method. We find the NN-doping can enhance the polarization and breakdown strength of BNT by suppressing the grain growth and restrained the reduction of Ti⁴⁺ to Ti³⁺. As a result, a high recoverable energy-storage density of 5.14 J/cm³ and its energy efficiency of 79.65% are achieved in BNT–0.5NN ceramic at 286 kV/cm. Furthermore, NN-doping can promote the densification to improve the optical transmittance of BNT, rising from ∼26% (x = 0.2) to ∼32% (x = 0.5) in the visible light region. These characteristics demonstrate the potential application of BNT–xNN as transparent energy-storage dielectric ceramics.     

Submicron-grained Yb:Lu2O3 transparent ceramics with lasing quality

We report on our recent progress of fabricating Yb³⁺-doped Lu₂O₃ transparent ceramics for 1 μm solid-state laser application. Well-dispersed 3.3 at.% Yb:Lu₂O₃ nanopowders were synthesized using a co-precipitation method. Without using any sintering aids, the Yb:Lu₂O₃ nanopowders could be densified by vacuum sintering at 1500°C/10 hours followed by HIPing at 1480°C/4 hours. Such obtained Yb:Lu₂O₃ ceramics had not only dense microstructure and submicron grain size of about 0.6 μm, but also in-line transmission of 80.0% at 600 nm. Preliminary continuous wave (CW) laser experiments with an uncoated Yb:Lu₂O₃ ceramic slab have demonstrated highly efficient CW laser oscillation at 1079.8 nm.     

Effect of sintering temperature on the microstructure and transparency of Nd,Y:CaF2 ceramics

1 at% Nd, 3 at% Y doped CaF₂ transparent ceramics were obtained by hot pressing at the sintering temperature varing from 500 to 800 °C under vacuum environment with co-precipitated CaF₂ nanopowders. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the obtained nanoparticles were single fluorite phase with grain size around 26 nm. Scanning electron microscopy (SEM) observations of the Nd, Y: CaF₂ ceramics indicated that the mean grain size of the ceramic sintered at 800 °C was about 748 nm. The influence of the temperature on the grain size, microstructure and optical transmittance was investigated. For the ceramic sintered at 800 °C, the transmittance was 85.49% at the wavelength of 1200 nm. The room temperature emission spectra of Nd: CaF₂ and Nd, Y: CaF₂ ceramics were measured and discussed.     

Co-precipitation of nano Mg–Y/ZrO2 ternary oxide eutectic system: Effects of calcination temperature

In the family of inorganic nanomaterials, zirconia is a highly promising functional ceramic with a high refractive index, hardness, and dielectric constant, as well as excellent chemical inertness and thermal stability. These properties are enhanced in nano-zirconia ceramics, because nanopowders have a small particle size, good morphology, and uniform and dispersive distribution. In this study, a co-precipitation process was proposed to synthesise highly dispersed MgO–Y₂O₃ co-stabilized ZrO₂ nanopowders. The effects of different calcination temperatures on the crystallisation degree and particle dispersion of zirconia nanopowders were characterised by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption using the Brunauer–Emmett–Teller (BET) theory, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The optimum synthesis conditions were obtained as follows: 6 h of high-energy planetary grinding and calcination at 800 °C in an electric furnace. Under these optimum conditions, the average particle size of the prepared powder was 28.7 nm. This process enriches the literature on the controllable preparation of Mg–Y/ZrO₂ nanopowders obtained by the co-precipitation method.