Mössbauer spectroscopic studies of Fe-substituted YIG

Compositional dependence of hyperfine parameters, determined through Mössbauer spectral analysis has been studied for Y_3−xFe_5+xO₁₂ (x = 0.0, 0.1, 0.3 and 0.5) garnet system at 300 K. The Mössbauer spectra have been fitted with three sextets in the ferrimagnetic state corresponding to Fe³⁺ ions at tetrahedral (d), octahedral (a) and dodecahedral (c) sites of the crystal structure. It is observed that isormershift, quadrupole shift and hyperfine field of d-site show no significant variation with Fe³⁺ concentration. The change in hyperfine fields of a- and c-sites with composition (x) has been explained on the basis of strength of exchange integrals, change in isomershift can be understood due to s-electron charge distribution and asymmetric displacement of oxygen ions surrounding the a- and c-sites seems to be responsible for observable quadrupole shift. The magneton number values obtained from magnetization and Mossbauer data are in agreement to those calculated using Neel's three sublattice model of ferrimagnetism.     

Characterization and optimization of magnetic garnet films for magneto-optical visualization of magnetic field distributions

Rare-earth iron garnet films with in-plane anisotropy grown on (111)-oriented substrates can be used as magneto-optical indicator films for visualization of magnetic leakage fields in nondestructive evaluation. The influence of Faraday rotation, Faraday ellipticity, absorption and film thickness on the performance of a magneto-optical indicator film is investigated. A new optimization method is introduced and compared with the method of contrast optimization. The theory is experimentally verified and an application example is presented.     

Compositional design,structure stability,and microwave dielectric properties in Ca3MgBGe3O12 (B = Zr,Sn) garnet ceramics with tetravalent cations on B-site

Two garnet-structured Ca₃MgBGe₃O₁₂ (B = Zr, Sn) ceramics with tetravalent cations at B-site were prepared by conventional solid state reaction. The crystal structure, microstructure evolution, and microwave dielectric performance were investigated using X-ray powder diffraction, Rietveld refinement, scanning electron microscopy, Raman spectroscopy, and infrared spectroscopy techniques. Dense Ca₃MgZrGe₃O₁₂ and Ca₃MgSnGe₃O₁₂ ceramics were obtained at sintering temperatures of 1420 and 1400 °C, respectively. The dielectric constant, unloaded quality factor, and temperature coefficient of resonance frequency of Ca₃MgZrGe₃O₁₂ were 10.80 ± 0.2; 79,600 ± 1000 GHz (f = 12.61 GHz); and ?66.8 ± 1 ppm/°C, respectively, and the corresponding values for Ca₃MgSnGe₃O₁₂ were 9.68 ± 0.2; 83,400 ± 1000 GHz (f = 14.19 GHz); and ?57.9 ± 1 ppm/°C, respectively. The dielectric performances of the two ceramics were compared by analyzing the ionic polarizability, packing fraction, and bond valence. The intrinsic dielectric properties were predicted by fitting the infrared reflectivity spectra.     

Scintillation properties of the Ce-doped multicomponent garnet epitaxial films

(Lu,Y,Gd)₃(Al,Ga)₅O₁₂:Ce garnet scintillator single crystalline films were grown onto LuAG, YAG and GGG substrates by liquid phase epitaxy method. Absorption, radioluminescence spectra and photoluminescence excitation, emission spectra, and decay kinetics were measured. Photoelectron yield, its dependence on amplifier shaping time and energy resolution were determined to evaluate scintillation performance. Most of the samples exhibited strong UV emission caused by trapped excitons and/or Gd³⁺ 4f–4f transition. However, emission spectrum of the best performing Gd₂YAl₅O₁₂:Ce is dominated by the Ce³⁺ fast 5d–4f luminescence. This sample has outperformed photoelectron yield of all the garnet films studied so far.     

Spreading and reaction behavior of CMAS-type silicate melts with multiphase Y and Gd aluminate-zirconate T/EBC materials

Thermal and environmental barrier coatings must be robust against attack by calcium magnesium aluminosilicate (CMAS, or CMFAS with iron) deposits, and coatings that produce thin, uniform reaction layers are desirable. The reactions of four multiphase coating compositions in the AlO_1.5–REO_1.5–ZrO₂ systems (RE = Gd or Y) with three model CMFAS deposits were studied. Following CMFAS exposure for 1 h at 1400°C, some samples exhibited thin, uniform CMFAS reaction product layers, while others were less uniform with pockets of deep reactions. Coating materials with higher AlO_1.5 content produced uniform reaction layers, while the most SiO₂-rich CMFAS was most likely to produce a non-uniform response. Apatite was formed in all cases, while the Y was more likely than Gd to form aluminosilicate garnet and cuspidine reaction products. The results are discussed in terms of implications for CMFAS-resistant T/EBC design.     

福建漳州复式岩体中晶洞石榴子石的裂变径迹研究

对福建漳州复式岩体中晶洞石榴子石的裂变径迹定年进行了可行性研究，经测定确认其为含锰量甚高的锰铝榴石，铀浓度变化范围为０．２－１．８μｇ／ｇ，裂变径迹年龄为７３．４±２．１Ｍａ，诱发裂变径迹和自发理解变径变迹的长度分别为１１．５±０．７μｍ和１１．０±０．８μｍ。     

Environment for rapidly creating interactive design tools

The Garnet toolkit was specifically designed to make highly interactive graphical programs easier to design and implement. Visual, interactive, user-interface design tools clearly fall into this category. At this point, we have used the Garnet toolkit to create three different interactive design tools: Gilt, a simple interface builder for laying out widgets; Lapidary, a sophisticated design tool for constructing application-specific graphics and custom widgets; and C32, a spreadsheet interface to constraints. The features of the Garnet toolkit that made these easier to create include use of a prototype-instance object system instead of the usual class-instance model, integration of constraints with the object system, graphics model that supports automatic graphical update and saving to disk of on-screen objects, separation of specifying the graphics of objects from their behavior, automatic layout of graphical objects in a variety of styles, and a widget set that supports such commonly used operations as selection, moving and growing objects, and displaying and setting their properties.     

Mössbauer spectroscopy of titanium-substituted iron garnets

The Mössbauer spectroscopy of polycrystalline Y_3?x Ca _x Fe_5?x Ti _x O₁₂ (x=0·2, 0·5, 0·7) garnets has been studied at room temperature. The hyperfine fields both at the octahedral and tetrahedral sites decrease with increasing titanium content. The hyperfine fields both ata andd-sites are linearly proportional to magnetization. The quadrupole splitting fora-site shows no dependence on Ti content while the quadrupole splitting ford-site increases slightly withx. The results are explained on the basis of lattice distortion due to Ti substitution ona-site.     

Mechanistic study of the effect of Ca–Sn co-doping on the microwave dielectric properties and magnetic properties of YIG

To investigate the crystal structure, electrical properties, and magnetic properties of Ca–Sn co-doped Y_3-xCa_xFe_5-xSn_xO₁₂ (x = 0.00–0.25 in steps of 0.05), solid-state reaction experiments, first principles calculations, and complex crystal bonding theoretical calculations were performed. The relative permittivity (ε_r) is strongly correlated with the average bond ionicity when Ca²⁺ is added. Furthermore, appropriate Sn⁴⁺ substitution significantly lowers the dielectric loss (tanδ_ε) associated with the lattice energy. The right amount of Ca–Sn co-doping can change the saturation magnetization (4πM_S) and improve the microscopic morphology of YIG, lowering the ferromagnetic resonance linewidth (ΔH) of YIG. The optimized microwave dielectric and magnetic properties are as follows: ε_r = 14.7, tanδ_ε = 4.15 × 10^?4, 4πM_S = 1680 G, and ΔH = 53 Oe for Y_2.8Ca_0.2Fe_4.8Sn_0.2O₁₂ sintered for 6 h at 1425 °C. Based on this material, a simple 3D model of a strip-line circulator with an insertion loss of less than 0.3 dB at each port and isolation greater than 20 dB in the 10–12 GHz range was developed, indicating the potential of the material for microwave high-frequency components such as circulators.     

Enable high reversibility of Fe/Cu based fluoride conversion batteries via interfacial gas release and detergency of garnet electrolytes

Garnet-type Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) electrolyte suffers from unstable chemical passivation under air exposure, responsible for the poor interfacial wettability and conductivity with Li metal. Instead of conventional methods to remove surface contaminants by mechanical polishing, acid etching and high temperature reduction, herein we propose a simple strategy of interfacial gas release and detergency to smartly convert Li₂CO₃ passivation layer into ion-conductive Li₃PO₄ domains at mild temperature (∼200 ℃). The in-situ formation of PH₃ vapor and its phosphorization enables a dramatic decrease of Li/garnet interfacial resistance down to 2 Ω cm² at room temperature (RT). The improved interfacial wettability and conductivity endow the symmetric cells with ultra-stable galvanostatic cycling over 1500 h and high critical current density of 2.6 mA/cm². The high coulombic efficiency of Li plating enables a high reversibility of solid-state NCM811/Li cells even under a low N/P ratio (∼4) and high cut-off voltage of 4.5 V at RT. The prototype of fluoride-garnet solid-state batteries are successfully driven as rechargeable system (rather than widely known primary battery) with high conversion capacity (400 ∼ 500 mAh/g) and high-rate performance (251.2 mAh/g at 3 C). This interface infiltration-detergency approach provides a practical solution to the achievement of high-energy solid-state Li metal batteries.