Garnet Research Articles

Thermal Conductivity of Calcium Aluminate and Complex Vanadates of Garnet Structure

The thermal conductivity of materials with the nonstoichiometric garnet structure, namely, of calcium aluminate Са12Al14O33±δ (both single crystal and ceramic) and doped vanadates Ca5Mg4–xMx(VO4)6 (M = Zn, Co; 0 ≤ x ≤ 4), in the temperature interval 50–300 K was studied by the steady state comparative-longitudinal thermal flux method. The compositions Ca5Mg4–xZnx(VO4)6, x =1, 3, 4, were studied in the temperature interval 298–573 K by the dynamic method. The effect of the defective structure on the thermal conductivity of the materials was discussed. The thermal conductivity of the materials is ~2 W m–1 K–1 at room temperature and above.

Realization of resistive and magnetization switching in sol-gel derived yttrium iron garnet thin films

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Sol-gel synthesis of Al- and Nb-co-doped Li7La3Zr2O12 solid electrolytes

A series of the Li7−y−3xAlxLa3Zr2−yNbyO12 (y = 0.1–0.25, x = 0–0.25) solid electrolytes were synthesized by sol-gel method and sintered at 1150 °C for 1 h. The phase analysis was done using X-ray diffraction method and Raman spectroscopy; the obtained compounds have a cubic structure Ia-3d. The Li6.6Al0.05La3Zr1.75Nb0.25O12 solid electrolyte has the highest total conductivity, 6.3·10−4 S cm−1 at 25 °C. The growth of Al content in Li6.75−3xAlxLa3Zr1.75Nb0.25O12 system leads to conductivity decreasing and activation energy growth. The conductivity descend can be associated with the decreasing of charge carriers (Li+) amount in the Li6.75−3xAlxLa3Zr1.75Nb0.25O12 structure. Li6.9−3xAlxLa3Zr1.9Nb0.1O12 and Li6.8−3xAlxLa3Zr1.8Nb0.2O12 solid electrolytes with a smaller addition of Nb have lower values of lithium-ion conductivity. Thus, it was concluded that high conductivity of Li6.6Al0.05La3Zr1.75Nb0.25O12 ceramic is caused by the optimal ratio of lithium vacancies and the number of charge carriers in the garnet structure. Thus, obtained solid electrolyte can be used in high-energy lithium and lithium-ion batteries.

A novel Al3+ modified Li6CaLa2Sb2O12:Mn4+ far-red-emitting phosphor with garnet structure for plant cultivation

A novel-far red emission Li6CaLa2Sb2O12 (LCLSO):Mn4+ phosphor was prepared by traditional high temperature solid state reaction method. The morphology, spectral characteristics and luminescence properties of the phosphors were all studied systematically. Based on the results, when x = 0.0045 (x represents the doping concentration of Mn4+), the emission intensity of LCLSO:xMn4+ phosphor reaches the maximum, and the concentration quenching occurs after the Mn4+ doping concentration exceeds 0.0045. In addition, the effect of Al3+-doped on the luminescent properties of the materials was also studied. The optimum doping concentration of Al3+ is y = 0.009 (y represents the doping concentration of Al3+), and the luminescence intensity of Mn4+ can be increased about 4 times. Moreover, the integrated luminescence intensity, the thermal activation energy, and decay time can be obtained via calculation. In summary, LCLSO:Mn4+, Al3+ phosphor exhibits good luminescence efficiency and thermal stability, and possesses the latent application foreground in plant growth lighting.

The History of the German Association for Crystal Growth

The History of the German Association for Crystal Growth

Melt-rock interaction between granitic pegmatites and hosting amphibolites from the Chiavenna Ophiolitic Unit (Tanno Pegmatitic Field, Central Alps, North Italy)

The Tanno pegmatitic field, placed southward of Chiavenna (Central Alps, Sondrio, Italy), develops a large number of subplanar dykes that crosscut the Chiavenna Unit, an ophiolitic complex mainly composed, in the study area, of amphibolite rocks. This study focuses on the contact between a pegmatitic dyke and the amphibolitic country rock. We distinguished four zones across the contact: I) inner amphibolite, II) contact amphibolite, III) contact pegmatite, IV) inner pegmatite. The inner amphibolite, not affected by melt-rock interaction, is composed of amphibole, phlogopite, ilmenite, titanite and rutile. Two amphibole generations occur, both of them showing a patchy compositional zoning. Amphibole I are Mg-hornblende, whereas Amphibole II have a pargasitic composition. The contact amphibolite shows an enrichment of mica belonging to the phlogopite-biotite series, titanite and the presence of fluorapatite and plagioclase (Ab45-60), that is absent in the inner amphibolite. Close to the contact, amphiboles display no zoning and gain an Mg-horneblenditic composition. The contact pegmatite has quartz, albitic plagioclase, garnet (almandine-spessartine series), muscovite, K-feldspar and fluorapatite. It shows a comb texture, with elongation of plagioclase crystals normal to the contact itself. Far from the contact, the inner pegmatite has an increasing grain-size and a less organized texture. In this zone several accessory phases occur, including gahnite, columbite-(Fe), monazite-(Ce), xenotime-(Y), uraninite and betafite. Whole rock analyses suggest that a chemical exchange, concerning both major elements and trace elements, occurred between the pegmatitic melt and the hosting amphibolite. A considerable increase of SiO2, Na2O and, to a lesser extent, of Al2O3 is observed from the amphibolite towards the pegmatite; K2O and CaO show a decrease at the same extent. The REE pattern in the pegmatite highlights an enrichment in HREE at the contact. Mineral chemistry confirms this trend with variations observable in plagioclase, gradually more albitic from the amphibolite to the pegmatite. Mineralogical characters and geochemical features allow to classify the Tanno pegmatite in the LCT (Lithium, Cesium, Tantalium) family. Based on the metamorphic peak conditions reported from the Lepontine Dome the ambient conditions during pegmatite intrusion were ca. 550°C and 5 kbar. The reduced thermal difference between pegmatite and wall rock explains the diffuse contact observed by X-ray micro-computed tomography. The collected data suggest a chemical interaction between melt and wall rock, according to the following reaction taking place in the amphibolite Amphibole I + Amphibole II + Ilmenite + Pegmatitic melt → Amphibole III + Plagioclase + Phlogopite + Titanite + Fluorapatite

Yellow Emission Obtained by Combination of Broadband Emission and Multi-Peak Emission in Garnet Structure Na2YMg2V3O12: Dy3+ Phosphor.

The fabrication and luminescent performance of novel phosphors Na2YMg2V3O12:Dy3+ were investigated by a conventional solid-state reaction method. Under near-UV light, the Na2YMg2V3O12 host self-activated and released a broad emission band (400–700 nm, with a peak at 524 nm) ascribable to charge transfer in the (VO4)3− groups. Meanwhile, the Na2YMg2V3O12:Dy3+ phosphors emitted bright yellow light within both the broad emission band of the (VO4)3- groups and the sharp peaks of the Dy3+ ions at 490, 582, and 663 nm at a quenching concentration of 0.03 mol. The emission of the as-prepared Na2YMg2V3O12:Dy3+ phosphors remained stable at high temperatures. The obtained phosphors, commercial Y2O3:Eu3+ red phosphors, and BaMgAl10O17:Eu2+ blue phosphors were packed into a white light-emitting diode (WLED) device with a near-UV chip. The designed WLED emitted bright white light with good chromaticity coordinates (0.331, 0.361), satisfactory color rendering index (80.2), and proper correlation to a color temperature (7364 K). These results indicate the potential utility of Na2YMg2V3O12:Dy3+ phosphor as a yellow-emitting phosphor in solid-state illumination.

Luminescence properties and efficient energy transfer investigations of inverse garnet-type Mg3Y2−x−yGe3O12:xTb3+, yEu3+ multicolor phosphor

Tb3+ and/or Eu3+ doped Mg3Y2Ge3O12 phosphors were synthesized successfully through solid-state reaction. The X-ray diffraction (XRD) patterns, photoluminescence (PL), fluorescence decay curve and energy transfer behavior of the samples were studied in detail. XRD patterns show all samples are attributed to inverse garnet structure. Under UV excitation, the singly doped phosphors with Tb3+ and Eu3+ ions showed green and red characteristic emission. The emission color of Mg3Y2Ge3O12:Tb3+, Eu3+ can be adjusted by the corresponding Tb3+–Eu3+ energy transfer, which also demonstrated excellent thermal stability at 448 K (78.09%). These results indicate that the Mg3Y2Ge3O12:Tb3+, Eu3+ phosphors will have potential use in n-UV pumped LED devices.

Synthesis and photoluminescence properties of new garnet-type red-emitting Li7La3-xZr2O12:xEu3+ phosphors

The structural and photoluminescence (PL) properties of as-synthesized and aged garnet-type Li7La3-xZr2O12:xEu3+ (0.02 ≤ x ≤ 0.10) phosphors for white light-emitting diode applications were systematically investigated. Li7La3Zr2O12 oxides satisfied the criteria, proposed by F. C. Hawthorne, for the formation of garnet structure. Rietveld refinement results showed that the as-synthesized Li7La3-xZr2O12:xEu3+ phosphors formed a tetragonal crystal structure (I41/acd space group) and emitted efficient red light. The aging of the Li7La3-xZr2O12:xEu3+ phosphors induced a gradual transition from the tetragonal to the cubic structure and formed a secondary phase Li2CO3, which yielded a substantial decrease in PL excitation and emission intensities.

Enhancing Luminescence and Controlling the Mn Valence State of Gd3Ga5-x-δAlx-y+δO12:yMn Phosphors by the Design of the Garnet Structure.

Gd3Ga5-x-δAlx-y+δO12:yMn solid solutions with improving luminescence properties were prepared via cation substitution and a controllable Mn valence state. The abnormal autoreduction from Mn4+ to Mn2+ ions was observed during the formation of Gd3Ga5-x-δAlx-y+δO12:yMn. The doped manganese ions occupy octahedral Ga3+(1) and Al3+(1) sites to form the Mn2+ luminescent center with red emission at 630 nm and Mn4+ luminescent centers with deep red light emission at 698 nm, respectively, matching well with the red light absorption of phytochrome (PR) and the far-red light absorption of phytochrome (PFR). With the design of the concentration of Al3+ and doped manganese ions, the photoluminescence (PL) of Mn4+/Mn2+ (corresponding to PFR/PR) can be tuned, which is very useful for controlling the plant growth. Moreover, the PL intensity of Gd3Ga5-x-δAlx-y+δO12:yMn can be increased by 6.8 times by substituting Al3+ for Ga3+. The thermal stability is also enhanced significantly. Finally, a series of warm white-light-emitting diodes (WLEDs) with good performance were fabricated using the as-prepared Gd3Ga5-x-δAlx-0.012+δO12:0.012Mn phosphor. The results show that the designed Gd3Ga5-x-δAlx-y+δO12:yMn phosphors have potential practical values in plant-growth light-emitting diodes (LEDs) and high-performance WLEDs. Moreover, our strategy not only provides a unique inspiration for tuning the valence states of Mn but also designs new advanced luminescent materials.

Crystal structure and photoluminescence properties of garnet−type as−synthesized and aged Li7La3−xZr2O12:xTb phosphors

The crystal structure and photoluminescence (PL) properties of Tb3+−activated garnet−type Li7La3−xZr2O12 garnet phosphors are reported. As−synthesized Li7La3−xZr2O12:xTb (0.02 ≤ x ≤ 0.10) phosphors form a tetragonal crystal structure and emit efficient green light due to the 5D4 → 7F5 transition of Tb3+. On the other hand, aged Li7La3−xZr2O12:xTb phosphors form mixed tetragonal and cubic crystal structures and contain a small amount of Li2CO3. The aged LLZO:xTb phosphors are brownish due to the oxidation of Tb3+ to Tb4+. The Tb4+ ions act as quenching sites for Tb3+ green emission owing to their strong absorption in UV–visible region. The aging significantly degrades emission intensities and color quality due to the presence of Tb4+ and Li2CO3.

Evaluation of temperature rise on the external root surface during the application of laser in root canals: An in vitro study

Background: Laser systems play an eminent role in endodontic treatment; however, some parameters should be investigated so that damage to the periodontal tissues can be prevented. Hence, in this context, the purpose of this study was to evaluate the temperature rises during the application of different power levels of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and erbium-doped yttrium aluminum garnet (Er:YAG) laser to the external root surface of permanent teeth. Materials and Methods: Sixty mandibular single-rooted premolars were selected and prepared chemomechanically. Nd:YAG laser (Group I) activated irrigation was performed in 30 teeth and remaining 30 received Er:YAG laser (Group II) treatment at three different power levels (1, 1.5, and 2.0 Watt), applied to 10 samples from each group. Type K thermocouple wire, along with a digital calibrated thermometer, was used to measure the temperature changes on the external root surface. Data were assessed with unpaired Student's t-test and two-way ANOVA. Results: With increasing power levels, temperature of external root surface also increased to some extent in both the groups. For apical third, at power level of 1.5 and 2 Watt, the difference in mean temperature between the two groups was found to be significant (6.30°C and 7.75°C; P = 0.005 and 9.11°C and 10.05°C; P = 0.036), whereas for middle third region, it was found that at power level of 2 Watt, the difference in mean temperature between the two groups was significant (6.69°C and 7.91°C; P = 0.007). Conclusion: Both Nd:YAG laser and Er:YAG laser at various power levels lead to rise in temperature on the external root surface, but the temperature changes in all the tested groups remained below the critical threshold.

Microleakage of novel glass ionomer restoration in cavities prepared by Er,Cr:YSGG laser: An in-vitro study

Aim: To compare the microleakage of novel materials containing glass ionomer, which are applied to standard class V cavities prepared by Er,Cr:YSGG (erbium, chromium-doped yttrium, scandium, gallium, and garnet) laser and by conventional diamond bur in primary teeth. Materials and Methods: Fifty non-carious primary molar teeth were randomly divided into five main groups and restored with various materials containing glass ionomers (Group 1: Equia System; Group 2: Fuji IX GP; Group 3: Fuji II LC; Group 4: Dyract Extra; and Group 5: Giomer). Each group was divided into two subgroups according to laser and conventional preparation methods. Results: As for the gingival margin, in terms of leakage values, no statistically significant difference was observed between drill and Er,Cr:YSGG laser although less microleakage values were obtained in Er,Cr:YSGG laser groups 1 and 4 (P > 0.05). Among groups prepared by drill, the lowest leakage rates observed at the gingival margin are Equia System, Giomer, Dyract Extra, Fuji II LC, and Fuji IX GP, respectively. Among groups prepared by Er,Cr:YSGG laser, the lowest leakage rates observed in the gingival edge are Equia System, Giomer = Dyract Extra, Fuji IX GP, and Fuji II LC, respectively. Conclusion: Occlusal and gingival microleakage scores were the lowest in the groups restored with Equia system in the cavities prepared by both diamond bur and laser system. Equia system consisting of high-viscosity glass ionomer cement and nano-filled surface coat G-Coat Plus materials could be used successfully in pediatric dentistry.

Absence of magnetic ordering in the spin liquid candidate Ca3Cu2GeV2O12

Typically, quantum spin liquid candidates can be found in materials with a combination of geometrical frustration along with low spin. Due to its spin of S = 1/2 the copper (II) ion is often present in the discussion on spin liquid candidates. The solid state compound Ca3Cu2GeV2O12 is a material that crystallizes in the garnet structure (s.g. #230, Ia-3d), where 3D frustration is known to occur. Heat capacity has shown a lack of magnetic ordering down to 0.35 K, confirmed with low temperature neutron diffraction to 0.07 K. This system displays a Weiss temperature of −0.93(1) K indicating net antiferromagnetic interactions and significant J1–J2 competition causing frustration. Using both neutron and x-ray diffraction along with heat capacity and magnetometry, the work presented here shows Ca3Cu2GeV2O12 has potential as a new spin liquid candidate.

Synthesis and characterization of Li7La3Zr2O12 via a novel solid-liquid route

Polycrystalline cubic Li6.5Al0.22La3Zr1.93O11.94 (LLZO) with garnet structure has been synthesized by solid-liquid method (SLM) with acrylic acid as organic complexing agent, and acetate sol coated nano-ZrO2 powders as template. The polymeric precursors are characterized by means of TG/DTA, the resultant powders and sintered LLZO pellets are characterized by ICP-OES, X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy. It is shown that the morphology of the powders is dependent on the preparation conditions such as molar ratio of acrylic acid to metallic ions (L/M) and the pH values. Prepared powders are purity, single phase, an ellipsoidal shape and a particle size of 2–4 μm with good neck connection. The ionic conductivity of sintered LLZO pellets at 1100 °C for 6 h at room temperature is 3.09 × 10−4 S cm−1 and the relative density is 94.1%. The solid-liquid method can lower the sintering temperature, greatly shortens holding time, and gets relatively good the ionic conductivity and it is suitable for mass synthesis of high performance LLZO powders with the advantages of less amount of organic reagent and friendly environment.

Li2CO3: A Critical Issue for Developing Solid Garnet Batteries

Solid garnet electrolytes are promising solid-state electrolytes because of their favorable ionic conductivity and high stability against Li metal anodes. However, their special surface chemistry greatly affects the practical applications whether in the form of garnet ceramic electrolytes (GCEs) or polymer/garnet electrolytes (PGEs). Even though large-scale production of garnet in an ambient atmosphere is possible, the passivated surface due to air exposure can lead to poor interfacial properties of GCEs with electrodes and low ionic conductivities of PGEs. Understanding the effects of air exposure on garnet structure stability, ion mobility, and interfacial configuration is crucial for better applications of solid garnet electrolytes. In this Perspective, we comprehensively recapitulate the reaction mechanisms and influencing factors of air-induced contaminations. Various surface engineering strategies tailoring garnet particles and/or pellets are reviewed. This Perspective provides insightful guidelines...

Structural Indicator to Characterize the Crystal-Field Splitting of Ce3+ in Garnets

The structure–property relationship is a hot research topic in both chemistry and material science. A structural descriptor has significant applications in machine learning and high-throughput screening for rapid estimations of material properties. In this work, we report a simple structural indicator to characterize the crystal-field splitting of Ce3+ ions in the garnet structure. The indicator is the interplanar distance of the octahedron, which is calculated as 2/√3 | x + y + z | · L, where L stands for the cell parameter and (x, y, z) are the oxygen coordinates in a specific form. The indicator value is correlated to the crystal-field splitting of Ce3+ in the lanthanide aluminum/gallium garnets and is able to reproduce the reverse garnet effect. By inspecting the polyhedral competition effect in the garnet structure, this indicator is found to be correlated to the tetragonal distortion of the dodecahedron, which determines the crystal-field splitting.

Synthesis and luminescence characterization of Ce3+ activated Y2CaAl2MgZr2O12 garnet phosphor for white light emitting diodes

A series of novel Ce3+ activated Y2CaAl2MgZr2O12 phosphors were synthesized via a modified solid-state method. The formation of garnet structure was clearly observed from the XRD studies. The elemental mapping images confirmed the homogeneous distribution of all elements in Y2CaAl2MgZr2O12:Ce3+. Y2CaAl2MgZr2O12:Ce3+ emitted greenish yellow emission peaking at 530 nm by absorbing blue light of 420 to 460 nm. The greenish yellow emission was due to the 5d-4f transition of Ce3+ ions. The optimum photoluminescence intensity was observed for 3 mol% concentration of Ce3+ ions. The thermal stability of photoluminescence emission of Y2CaAl2MgZr2O12:0.03Ce3+ was also investigated at 300 to 480 K and the activation energy was calculated to be 0.32 eV. Commercial red (Sr, Ca)AlSiN3:Eu phosphors blended with Y2CaAl2MgZr2O12:0.03Ce3+ and coated on blue emitting LED chips to fabricated white light emitting diodes (WLEDs). The electroluminescence spectra of the fabricated WLEDs exhibited pure white chromaticity (0.36, 0.37) with high CRI of 94 and low CCT of 4381 K. The spectral characteristic results indicated a promising garnet phosphor for blue excited white light emitting diode applications.

A novel tungstate Li3Nd3W2O12 with garnet structure for low-temperature cofired ceramic technology

Microwave dielectrics sintered at low temperature are pursued for energy saving and cofiring with cost-effective metallic electrodes (e.g. Cu, Ag and Al). In this study, a novel tungstate low-firing microwave dielectric ceramic, Li3Nd3W2O12, which can realise co-firing with Ag electrode at 940 °C, was synthesised by the conventional solid-state reaction method. According to the X-ray diffraction and Rietveld refinement results, Li3Nd3W2O12 crystallised in the garnet structure with a space group of Ia3¯d and W6+ cations fully occupying the octahedral-coordinated site. The optimum microwave dielectric properties with permittivity of ∼9.8, quality factor of ∼36,800 GHz and temperature coefficient of resonant frequency of ∼ –30 ppm/°C were obtained after sintered at 940 °C. A near-zero temperature coefficient of resonant frequency of +3.6 ppm/°C was achieved in 0.96Li3Nd3W2O12-0.04CaTiO3 ceramics. These properties make tungstate Li3Nd3W2O12 a promising candidate for low-temperature co-fired ceramic technology.

All-Solid-State Electrospun Poly(vinylidene fluoride-co-hexafluoropropylene)/Li7.1La3Ba0.05Zr1.95O12 Nanohybrid Membrane Electrolyte for High-Energy Li-Ion Capacitors

Herein, we prepared all-solid-state electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/Li7.1La3Ba0.05Zr1.95O12 nanohybrid membrane electrolytes (esHPMEs) by an electrospinning ...