Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Fabrication of oxide-based near infrared-shielding coatings for a smart window to prevent infrared-induced photoaging in human skin

Oxide-based near infrared (IR)-shielding coatings consisting of quarter‐wave stacks of oxygen-deficient tantalum oxide (Ta₂O_5?x) and silicon oxide (SiO₂) multilayers and tin-doped indium oxide (In₂O₃) (ITO) films with the thicknesses of 200–600 nm can block the passage of IR-A (wavelength: 760–1400 nm) and IR-B (wavelength: 1400–3000 nm) radiation, respectively. In this study, the optical properties and microstructure of these oxide-based IR-shielding coatings were investigated. Transmission electron microscopy images indicated that amorphous Ta₂O_5?x/amorphous SiO₂ multilayers were uniform and dense. ITO films were found to be highly crystalline and show carrier concentrations of up to 7.1 × 10²⁰ cm^?3, resulting in the strong IR-B optical absorption due to the plasma excitation of the free carriers. Oxide-based IR-shielding coatings with an ITO thickness of 420 nm were found to have near-IR shielding rates of >90% and an average visible light transmittance of >70%. The effects of IR on human keratinocytes were studied to evaluate the IR-induced photoaging in human skin. It was found that the downregulation of cellular proliferation and the enhancement of senescence-associated β-galactosidase activity induced by IR irradiation were significantly inhibited by oxide-based IR-shielding coatings. Thus, this study provides a facile method for the development of coatings for smart windows with high IR-shielding ability and high visible light transmittance.     

Highly transparent yttria ceramics with Nb2O5/Ta2O5 as novel sintering additives by pressureless vacuum sintering

Highly transparent yttria ceramics were fabricated by pressureless sintering with Nb₂O₅ or Ta₂O₅ as a novel sintering additive. The optical transmittance, microstructural evolution, and thermo-mechanical properties of the samples were investigated. The optimal doping concentrations of Nb₂O₅ and Ta₂O₅ are 0.3 and 0.2 at.%, respectively, which are much lower compared to those of previously reported counterparts. The transmittance of the sample with 0.3 at.% Nb₂O₅ reaches 81.6% at 1100 nm and 72.4% at 400 nm (2 mm in thickness), similar transmittance was obtained in the sample with 0.2 at.% Ta₂O₅. The microhardness (∼7 GPa), fracture toughness (∼0.85 MPa·m^1/2), and biaxial strength (∼200 MPa) of the present samples were confirmed to be comparable or even better compared to those of previously reported transparent yttria ceramics fabricated by pressureless sintering. Furthermore, the present samples, by virtue of the low doping concentrations, possessed relatively high thermal conductivity values (>10 W/m·K), which substantially guaranteed high thermal shock resistance.     

Influence of Ag incorporation on the structural,optical and electrical properties of ITO/Ag/ITO multilayers for inorganic all-solid-state electrochromic devices

Indium tin oxide/silver/indium tin oxide (ITO/Ag/ITO, IAI) multilayer structures were prepared by DC magnetron sputtering as a conductive transparent electrode for inorganic all-solid-state electrochromic devices. A thin layer of silver (Ag) with various thicknesses was inserted between two layers of ITO films. The XRD and SEM results revealed that the microscopic morphology of Ag film was closely related to the thickness. Besides, the electrical and optical properties of the IAI multilayers were significantly influenced by the Ag layer thickness. The optimized IAI multilayers demonstrated the best combination of electrical and optical properties with a figure of merit of 54.05 (sheet resistance of 6.14 Ω/cm²and optical transmittance of 90.83%) when the Ag film was 10 nm thick. In order to evaluate the IAI multilayers as a transparent electrode for electrochromic applications, two ECDs with the structures of ITO/NiO_x/LiPON/WO₃/ITO and ITO/NiO_x/LiPON/WO₃/IAI were prepared, and their electro-optical properties were characterized by cyclic voltammetry (CV), chronoamperometry (CA) and spectroscopic measurements. Compared with ECD the pure ITO top electrode (ITO/NiO_x/LiPON/WO₃/ITO), the ECD with the IAI top electrode (ITO/NiO_x/LiPON/WO₃/IAI) presented a slightly smaller optical modulation amplitude, but a faster switching speed. All our findings indicate that the IAI multilayer structure is a promising alternative to the ITO thin film for inorganic all-solid state electrochromic applications.     

Thermally stable and transparent F-doped SnO2 (FTO) /Ag/FTO films for transparent thin film heaters used in automobiles

We investigated the characteristics of F-doped SnO₂ (FTO)/Ag/FTO films prepared using thermal evaporation at room temperature for the application of the as-formed films in transparent thin film heaters (TFHs) of automobiles. To optimize the electrical and optical properties of the FTO/Ag/FTO multi-layer, the figure of merit (FoM) values of the FTO/Ag/FTO multi-layers were compared as a function of the thickness of the Ag and FTO layers. The sheet resistance and optical transmittance of the FTO/Ag/FTO multi-layer were primarily affected by the Ag inter-layer and bottom/top FTO thicknesses, respectively. At optimized Ag (10 nm) and FTO (40 nm) thicknesses, we fabricated a FTO/Ag/FTO electrode with a sheet resistance of 8.00 Ohm/square, an optical transmittance of 83.04 % at a visible wavelength (400–800 nm) and a FoM value of 19.49 Ohm^-1. The TFHs comprising the optimal FTO/Ag/FTO electrode exhibited a saturated temperature of 117 °C at a low operating direct current of 6 V, owing to the low sheet resistance. In addition, the FTO/Ag/FTO-based TFHs exhibited thermally stable performances owing to the stability of the bottom and top FTO electrodes. The performance of the FTO/Ag/FTO-based TFHs demonstrated that the thermally evaporated FTO/Ag/FTO multi-layer is a promising, stable, and transparent electrode material for application in the front window TFHs used in automobiles.     

Silver nanoparticles enhanced photoluminescence and the spectroscopic performances of Nd3+ ions in sodium lanthanum borate glass host: Effect of heat treatment

Silver nanoparticles (NPs) impact on the emission attributes of Nd³⁺ activated Na₂O–La₂O₃–B₂O₃ vitreous host matrix has been studied and discussed in detail. The effect of nucleation and growth of Ag NPs occurred due to the different heat–treatment durations at the temperature of 450 °C has been discussed. Transmission electron microscopy measurement revealed the formation of spherically shaped Ag NPs in the studied samples. The median Ag NPs size was increased from 2 to 9 nm with heat–treatment durations. Utilizing the absorption spectra of Nd³⁺ ions, the phenomenological Judd–Ofelt (J–O) parameters (Ω_{λ= 2, 4, 6}) were estimated. The optimized luminescence intensity at 1056 and 875 nm have realized for 10 h of annealing at 450 °C, with an enhancement factor of 160%. Moreover, the quantum efficiency for 1056 nm increased steadily with the heat–treatment duration. The stimulated emission cross–section and gain bandwidth for 1056 nm laser transition has shown to be 2.92 × 10^?20 cm² and 9.19 × 10^?26 cm³ for the Ag NPs embedded glass–composite. The results exemplifies the suitability of Ag NPs embedded glass–composites for the fabrication of compact solid–state infrared lasers.     

Electrical and optical characteristics of transparent conducting Si-doped ZnO/hole-patterned Ag/Si-doped ZnO multilayer films

Hole-patterned Ag layers were first used to form Si-doped ZnO (SZO)/hole-patterned Ag/SZO multilayers and their optical and electrical properties were characterized. Unlike conventional oxide/metal/oxide multilayers, all samples exhibited two characteristic features: (i) a sinusoidal wavelength dependence of the transmittance with double maxima, and (ii) undulation in the visible transmittance, but not in the infrared transmittance. With increasing SZO thickness, the transmittance maxima were red-shifted, and the visible transmittance window widened. The carrier concentration decreased from 7.42×10²² to 2.4×10²² cm⁻³, and the sheet resistances varied from 7 to 10 Ω/sq with increasing SZO thickness. Haacke's figure of merit (FOM) was calculated for the SZO-based multilayer films. The 40 nm-thick SZO multilayers had the highest FOM of 15.9×10^–3 Ω^–1. Finite-difference time-domain (FDTD) simulations were undertaken to interpret the measured transmittance. Based on the FDTD simulations, the undulating transmittance was attributed to surface plasmon-polaritons.     

Colored films produced by electron beam deposition from nanometric TiO2 and Al2O3 pigment powders obtained by modified polymeric precursor method

Synthesis and the characterization of TiO₂:5%Co (green), TiO₃:5%Fe (brown-reddish), TiO₂:2%Cr (brown), Al₂O₃:5%Co (blue), Al₂O₃:5%Fe (brown-reddish) and Al₂O₃:2%Cr (light green) nanometric pigment powders using polymeric precursor (modified Pechini's method) is reported. Colored thick films were deposited on amorphous quartz substrates by electron beam physical vapor deposition (EB-PVD) using pellets of the pigment powders as target. The evaporation process was carried out in vacuum of 4 × 10⁻⁶ Torr and the amorphous quartz substrates were kept at 350 °C during deposition. The TiO₂-based pigment powders presented crystalline anatase phase and the Al₂O₃-based pigment powders showed corundum phase, investigated by X-ray diffraction (XRD). The average particle size of the pigment powders was about 20 nm, measured by scanning electron microscopy with field emission gun (SEM-FEG). Diffuse reflectance spectra and colorimetric coordinates L¹, a¹, b¹ using the CIE-L¹a¹b¹ method are shown for the pigment powders, in the 350–750 nm range. The colored thick films were characterized by transmittance (UV–Vis) and atomic force microscopy (AFM). The average film roughness was ∼5.5 nm and the average grain size obtained in the films was around 75 nm. Films with thickness from 400 nm to 690 nm were obtained, measured by talystep profiler. Transmission spectra envelop method has been used to obtain refractive index and thickness of the Al₂O₃ colored thick films.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Enhancing optical and electrical properties of Al-doped ZnO coated polyethylene terephthalate substrates by laser annealing using overlap rate controlling strategy

Aluminum-doped zinc oxide (AZO) layers were deposited on polyethylene terephthalate (PET) flexible substrates and optimized by laser annealing using a 532 nm nanosecond pulsed laser. Effects of overlap rates, i.e. laser spot overlap rate (SO_R) and laser scan line overlap rate (LO_R), on AZO/PET films were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), UV–visible transmittance spectra and digital four-point probe instrument, respectively. Laser annealing could greatly enhance grain crystallinity, increase crystallite size and avoid damage to the PET flexible substrates, thus effectively enhance transmittance and conductivity of the films. The results showed that the AZO/PET film annealed by using 85% SO_R and 60% LO_R presented the highest average visible transmittance of 76.2% and the lowest resistivity of 1.95×10⁻³ Ω cm, which respectively improved by approximately 23% and 75% compared to those of the as-deposited AZO/PET film. This work may be of great importance from the viewpoint of performance optimization of transparent conductive oxide (TCO) flexible films.     

Elucidating the influences of Tantalum (V) oxide in Bi2O3–TeO2–ZnO ternary glasses: An experimental characterization study on optical and nuclear radiation transmission properties of high-density glasses

We report the optical and experimental gamma-ray and neutron attenuation properties of tantalum pentoxide reinforced Bi₂O₃–TeO₂–ZnO ternary glasses with a nominal composition of 10Bi₂O₃–70TeO₂-(20-x)ZnO-xTa₂O₅ (where x = 0,2,4, and 6 mol%). Measurements of transmittance and absorbance spectra for all of the synthesized samples are performed with Analytik Jena Specord 210 plus device between the range of 190–1100 nm. Moreover, ¹³³Ba and ²⁴¹Am/Be sources are utilized for experimental gamma-ray and neutron attenuation studies of BTZT glasses. According to results, the absorption edge is consistently moved from 380 nm to 390 nm as a result of ZnO/Ta₂O₅ translocation. In addition to decrease in optical band gap values of glass series, the fact that doping the structure containing Ta₂O₅ is lead to an increase in Urbach energies. The obtained irregularity through an increasing Ta₂O₅ additive is also changed the overall nuclear radiation attenuation properties of the BTZT glasses. The gamma-ray attenuation properties are obviously enhanced within the energy range of ¹³³Ba radioisotope. The attenuation properties against fast neutron emitted from ²⁴¹Am/Be were significantly enhanced through increasing Ta₂O₅ contribution. It can be concluded that BTZT6 glass sample may be regarded as a beneficial glass composition for multifunctional applications. It can be also concluded that ZnO/Ta2O5 translocation in Bi₂O₃–TeO₂–ZnO ternary glasses may be regarded as a monotonic tool where the neutron attenuation properties should be strengthened in addition to gamma attenuation properties.     

Effect of Ta2O5 Substituting on Thermal and Optical Properties of High Refractive Index La2O3–Nb2O5 Glass System Prepared by Aerodynamic Levitation Method

High refractive index glasses with nominal composition of 0.35La₂O₃–(0.65?x)Nb₂O₅–xTa₂O₅ (x ≤ 0.35) were prepared by aerodynamic levitation method. The effect of Ta₂O₅ substituting on their thermal and optical properties was investigated. All the glasses obtained were colorless and transparent. Differential thermal analyzer results show that as the content of Ta₂O₅ increased, the thermal stability of the glasses increased but the glass‐forming ability decreased. The transmittance spectra of all the obtained glasses exhibited a wide transmittance window ranging from 380 to 5500 nm. As the content of Ta₂O₅ increased, the refractive index of the glasses was enhanced from 2.15 to 2.21 and the dispersion was reduced with the Abbe number increasing from 20 to 27.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

ZnMgBeO/Ag/ZnMgBeO transparent multilayer films with UV energy bandgap and very low resistance

The ZnMgBeO/Ag/ZnMgBeO multilayer structures were sputter grown and their electrical and optical properties have been investigated in detail. Results indicated that the ZnMgBeO(30 nm)/Ag(10 nm)/ZnMgBeO(30 nm) optimum structure shows energy bandgap of ~4.5 eV, electrical resistivity of ~6.5×10⁻⁵ Ωcm, and optical transmittance of 78–90% over the visible wavelength range and 74–90% over 300–400 nm range, representing a significant improvement over the previously reported transparent conducting films. High resistivity (~0.12 MΩcm) of the ZnMgBeO layer did not critically affect the conductivity of the multilayer, because the Ag films act as the conducting path. It was also observed that the properties were substantially deteriorated at the Ag thickness of 5 nm, as the Ag film is only partly continuous, resulting in very rough interfaces and surfaces.     

Physico-chemical and antimicrobial properties of Ag/Ta2O5 nanocomposite coatings

Surface modification of surgical instruments is carried out in order to improve the antibacterial performance against the surgical site infections. Healthcare acquired infections (HAI) and Nosocomial infections are one of the leading causes of complications/deaths after surgery. There is an increasing trend of antibiotic resistance in bacteria such as, vancomycin-resistant Enterococcus (VRE), carbapenem-resistant Enterobacteriaceae (CRE), multi-drug-resistant Mycobacterium tuberculosis (MDR-TB), methicillin-resistant Staphylococcus aureus (MRSA), and Neisseria gonorrhoeae. Thus, surfaces that counteract the adherence and growth of bacteria are employed to avoid the infections. In present study, stainless steel 316 L (SS 316 L) was coated with Silver/Tantalum oxide (Ag/Ta₂O₅) nanocomposite using reactive magnetron sputtering. The as-sputtered Ag/Ta₂O₅ nanocomposite (a-Ag/Ta₂O₅) film was crystallized via thermal treatment at 400 °C. Due to the annealing, the AgNPs migrated to the surface through the columnar paths of the a-Ag/Ta₂O₅. Thus, the crystallized layer (c-Ag/Ta₂O₅) exhibited 302% improvement in adhesion strength and enhanced hydrophopibicity. The c-Ag/Ta₂O₅ also demonstrated excellent antibacterial performance against Staphylococcus aureus (NCTC 6571) (gram-positive bacteria) and Escherichia coli (ATCC 15597) (gram-negative bacteria) according to the inhibition zone measurements. These results suggest that c-Ag/Ta₂O₅ deposition on SS 316 L substrate has a high potential to serve as an adherent, antibacterial layer on the surgical tools, in order to resist surgical site infections.     

Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Influence of post-deposition annealing on electrical and optical properties of (Ta2O5)1-x - (TiO2)x thin films,x ≤ 0.08

Tantalum (Ta) and titanium (Ti) metal targets were direct current (DC) magnetron sputtered in the oxygen environment by varying its relative areas to deposit (Ta₂O₅)_1-x- (TiO₂)_x (TTO_x) thin films, with x = 0, 0.03, 0.06, and 0.08, onto the boron-doped p-silicon (1 0 0) and optically polished quartz substrates, at room temperature; and were annealed at 500, 600, 700, and 800 °C, for 1.5 h. The thin films annealed at and above 600 °C show the Ta₂O₅ structure. The leakage current density and capacitance-voltage (C–V) characteristics were measured for TTO_x, x ≤ 0.08, assisted Ag/TTO_x/p-Si metal– oxide– semiconductor (MOS) structures. The leakage current density was found minimum, for the films annealed at 800 °C, for all the prepared TTO_x films, x ≤ 0.08. The minimum leakage current density 1.6 × 10^?8 A/cm², at 3.5 × 10⁵ V/cm electric field, was observed for x = 0.03, annealed at 800 °C, among the prepared compositions. The prepared TTO_0.03 films, annealed at 700 °C show maximum dielectric constant 39, at 1 MHz. The optical parameters, viz., refractive index (n), extinction coefficient (k), and optical band gap (E_g) of the films, with x = 0.03, prepared on quartz substrates, were determined from their optical transmittance plots. The values of n and k of the crystalline films were observed increasing from 2.123 to 2.143, and 0.099 to 0.130, respectively, at 550 nm wavelength; and E_g decreasing from 3.95 to 3.89 eV with the increasing annealing temperature, from 600 to 800 °C. Ohmic emission, in the lower electric field; Schottky and space-charge- limited current conduction mechanisms, in the intermediate to higher electric fields, were generally envisaged from the current-voltage characteristics in the prepared Ag/TTO_0.03/p-Si structures.     

Sintering,thermal expansion,and thermal transport properties of A4Ta2O9 (A= Ca,Mg) tantalates

Searching for new oxides with low thermal conductivity and high thermal expansion coefficients (TECs) as thermal barrier coatings (TBCs) is vital for the development of highly efficient gas turbines and aeroengines. We report the densification sintering, high TECs, and low thermal conductivity of A₄Ta₂O₉ (A = Ca, Mg) tantalates. The best sintering temperature of dense A₄Ta₂O₉ ceramics was determined via an optical contact angle tester, and samples with a relative density of 99.8% were synthesized via spark plasma sintering (SPS). The hardness (9–10 GPa), Young's modulus (172.7–211.8 GPa) and fracture toughness (1.5–1.6 MPa m^1/2) of the A₄Ta₂O₉ ceramics are primarily affected by the bonding strength. Furthermore, we studied the thermal transport properties of A₄Ta₂O₉. The low thermal conductivity (1.78–1.93 W m^?1 K^?1 at 900 °C), extraordinary phase stability, and high TECs (11.4–11.8 × 10^?6 K^?1 at 1200 °C) of A₄Ta₂O₉ ceramics make them candidate TBCs with high operating temperatures.     

The effect of co-substitution on the microwave dielectric properties of Ba6-3xNd8+2xTi18O54(x=2/3) ceramics

In this work, the microwave dielectric properties of Ba₄(Nd_1-yBi_y)_28/3Ti_18-x(Al_1/2Ta_1/2)_xO₅₄(0≤x≤2, 0.05≤y≤0.2) ceramics co-substituted by A/B-site were studied. Firstly, (Al_1/2Ta_1/2)⁴⁺ was used for substitution at B-site. At 0≤x≤1.5, the above mentioned ceramic was found to exist in single-phase tungsten bronze structure, but at x = 2.0, the secondary phase appeared. Although the dielectric constant decreased by doping the (Al_1/2Ta_1/2)⁴⁺, but the quality factor was observed to improve by 40% and the temperature coefficient of resonant frequency decreased by 75%. Based on the above results, Bi³⁺ was introduced to Ba₄Nd_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄. The introduction of Bi³⁺ reduced the sintering temperature, greatly improved the dielectric constant, and ultimately decreased the temperature coefficient of resonant frequency, but it led to deterioration of quality factor. At last, with appropriate site-substitution content control (x = 1.0,y = 0.15), excellent comprehensive properties (ε_r = 89.0, Q × f = 5844 GHz @ 5.89 GHz，TCF = +8.7 ppm/°C) were obtained for the samples sintered at 1325 °C for 4 h.     

Preparation and optical properties of samaria-doped yttria-stabilized zirconia single crystals

Single crystals of yttria-stabilized zirconia (YSZ) doped with various concentrations of Sm₂O₃ were synthesized by the optical floating zone method, and their structure and spectroscopic properties characterized using powder X-ray diffraction (XRD), optical absorption, and luminescence measurements. XRD showed that the cubic phase of ZrO₂ was stabilized by addition of Y₂O₃ and a series of absorption peaks characteristic of Sm³⁺ was detected by UV-visible absorption spectroscopy. Three phenomenological J-O oscillator strength parameters Ω_t (t = 2, 4, 6) were calculated to evaluate the local structure and bonding in the vicinity of the Sm³⁺ for the 0.75 mol% Sm₂O₃: YSZ sample. These were in order of Ω₂ < Ω₄ < Ω₆ with values of Ω₂ = 5.46 × 10⁻²⁰ cm², Ω₄ = 10.70 × 10⁻²⁰ cm², and Ω₆ = 12.67 × 10⁻²⁰ cm², and indicate a relatively high symmetry and low covalent character for the Sm-O bond at the Sm³⁺ sites in the YSZ matrix. Photoluminescence spectra recorded under an excitation of 404 nm showed four emission bands centered at 571 nm, 621 nm, 652 nm, and 716 nm corresponding to the transitions ⁴G_5/2→⁶H_j (j = 5/2, 7/2, 9/2, 11/2). The transition probability, lifetime, and branching ratio obtained from the emission spectrum of the 0.75 mol% Sm₂O₃: YSZ crystal showed that YSZ is a potential host for Sm³⁺ to achieve a reddish-orange laser output, and the Sm³⁺-modified YSZ crystals have a possible use in reddish-orange laser and lighting devices.