Amorphous Yttrium Research Articles

Enhanced magnon transport through an amorphous magnetic insulator

Conduction of spin currents in disordered insulating antiferromagnets has recently been at the center of scientific debate with both long-range spin transport or no spin transport at all observed experimentally. In this study, ferromagnetic resonance has been used to probe the transmission of ac spin current through thin amorphous yttrium iron garnet (YIG) layers. The spin current is found to be mediated by evanescent spin waves with a penetration length four times larger than that of previous studies of amorphous YIG, even exceeding the spin penetration length of crystalline NiO. Published by the American Physical Society 2024

Dual-Core Ce: YAG-Derived Silicate Scintillation Fiber for Real-Time X-Ray Detection

A dual-core Ce:YAG-derived scintillation fiber (DCSF) was proposed conceptually, simulated numerically, and prepared experimentally by the modified molten core method (MCM) for the first time, of which, the core material is amorphous yttrium aluminosilicate glasses and the cladding material SiO2. Theoretically, it is found that such kind of DCSF exhibits very low inter-core crosstalk with the help of finite element simulation analysis, which may result from the high index difference of ∼0.097 between core and cladding. The average decay lifetime of the prepared DCSF are 31.4 ns and 36 ns at 350 nm and 500 nm, which are shorter than those of its Ce:YAG bulk crystal counterpart. Radiation monitoring was demonstrated by an all-fiber detection system. The radiation response of the DCSF bundle was also investigated, whose radio-luminescence response intensity is ∼1.66 and ∼1.12 times higher than that of the single-core fiber bundles with similar core-diameter and with similar core-area, respectively. In conclusion, with radiation detection performance improvement enabled by space division multiplexing capability, the DCSF not only provides a solution for the dilemma between low transmission loss and high optical yield, but also makes a substantial step towards the development of practical and reliable radiation detectors.

Defect control and optical performance of yttrium orthovanadate nanocrystals via a facile pH-sensitive synthesis

Nanocrystalline YVO4 powders have been synthesized via a facile co-precipitation method, which has been investigated over the wide pH range from 4 to 13. XRD patterns indicated that the phase structure purity of the precipitation is influenced by the pH value. The reaction mechanism of YVO4 crystal was suggested to illustrate the development stages beginning with precipitates to form impure amorphous phase structures such as amorphous yttrium polyvanadate and hydrous Y(OH)3. SEM and TEM techniques were performed to observe the changes of the morphology and size by adjusting the pH conditions after YVO4 nanocrystals were sintered under ambient conditions at 600 °C for 2 h. Luminescence properties showed that the self-activated emission of YVO4 matrix material shows an obvious peak at 486 nm in the 400–650 nm wavelength range, attributing to the charge transfer in the vanadate groups. With decreasing the pH value, the diffuse reflectance spectra of YVO4 nanocrystals demonstrated that the energy gap Eg showed a red-shift trend mainly ascribed to the oxygen vacancies. Moreover, the luminescence emission intensity of YVO4 nanocrystals increases obviously after sintering treatment, which can be explained by the sintering-induced grain growth and improved surface band bending due to the dehydration or the removal of carbonate species. The findings of this study could provide new insights into the understanding of the reaction mechanism of YVO4 crystal with variable optical band gap and offer an opportunity for realizing tunable optical performance by defect structure regulation for laser and optoelectronics applications.

Electrical, optical, and magnetic properties of amorphous yttrium iron oxide thin films and consequences for non-local resistance measurements

We present magnetic characterization, charge resistivity, and optical photoluminescence measurements on amorphous yttrium iron oxide thin films (a-Y–Fe–O), with supporting comparisons to amorphous germanium (a-Ge) films. We measured magnetic properties with both SQUID magnetometry and polarized neutron reflectometry. These results not only confirm that a-Y–Fe–O is a disordered magnetic material with strong predominantly antiferromagnetic exchange interactions and a high degree of frustration, but also that it is best understood electrically as a disordered semiconductor. As with amorphous germanium, a-Y–Fe–O obeys expectations for variable-range hopping through localized electron states over a wide range of temperature. We also clarify the consequences of charge transport through such a semiconducting medium for non-local voltage measurements intended to probe spin transport in nominally insulating magnetic materials. We further compare non-local resistance measurements made with “quasi-dc” automated current reversal to ac measurements made with a lock-in amplifier. These show that the “quasi-dc” measurement has an effective ac current excitation with frequency up to approximately 22 Hz, and that this effective ac excitation can cause artifacts in these measurements including incorrect sign of the non-local resistance. This comprehensive investigation of non-local resistance measurements in a-Y–Fe–O shows no evidence of spin transport on micrometer length scales, which is contrary to our original work, and in line with more recent investigations by other groups.

Highly Thermally Resilient Dual‐Mode (Digital/Analog) Amorphous Yttrium Fluoride Memristors Exhibiting Excellent Symmetric Linearity

This paper describes the first use of vacuum-deposited YF3 films as active materials in memristors. These YF3 memristors function with extraordinary dual digital/analog operation modes. In both modes, the memorization states are all non-volatile, with long retention times (up to 106 s). In the analog mode, the memristors achieve a stable series of consecutive cycles of 64-level potentiation and depression, with large ON/OFF resistance ratios (up to 7.2), and extraordinarily balanced linearity. With these YF3 memristors, an excellent recognition accuracy of 97% in the classification of handwritten digits is achieved. Time-of-flight secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, and valance change memory modeling to examine the switching mechanism of YF3 are used, discovering that fluorine vacancy species are responsible for the memristor behavior. Excellent high-temperature stability during both operation and state preservation suggests that these YF3 memristors might find applicability in neuromorphic computing under relatively harsh conditions.

Nd3+-doped amorphous calcium yttrium silicate ceramic powder for near-infrared thermometry

Nd3+-doped amorphous calcium yttrium silicate ceramic powder for near-infrared thermometry

Fabrication and Characterization of Transparent and Scratch-Proof Yttrium/Sialon Thin Films.

Transparent and amorphous yttrium (Y)/Sialon thin films were successfully fabricated using pulsed laser deposition (PLD). The thin films were fabricated in three steps. First, Y/Sialon target was synthesized using spark plasma sintering technique at 1500 °C in an inert atmosphere. Second, the surface of the fabricated target was cleaned by grinding and polishing to remove any contamination, such as graphite and characterized. Finally, thin films were grown using PLD in an inert atmosphere at various substrate temperatures (RT to 500 °C). While the X-ray diffractometer (XRD) analysis revealed that the Y/Sialon target has β phase, the XRD of the fabricated films showed no diffraction peaks and thus confirming the amorphous nature of fabricated thin films. XRD analysis displayed that the fabricated thin films were amorphous while the transparency, measured by UV-vis spectroscopy, of the films, decreased with increasing substrate temperature, which was attributed to a change in film thickness with deposition temperature. X-ray photoelectron spectroscopy (XPS) results suggested that the synthesized Y/Sialon thin films are nearly homogenous and contained all target’s elements. A scratch test revealed that both 300 and 500 °C coatings possess the tough and robust nature of the film, which can resist much harsh loads and shocks. These results pave the way to fabricate different Sialon doped materials for numerous applications.

Methods of investigation transformation kinetics of yttrium carbonate hydroxide in citric acid solution into yttrium citrate dihydrate

A method of synthesis crystalline yttrium citrate dihydrate was proposed as a result of the transformation of the freshly precipitated basic yttrium carbonate phase in a citric acid solution. The synthesis time was determined on the basis of composition analysis, structure and thermogravimetric studies of samples taken during the synthesis. The research methods used have shown that in the initial stage of the synthesis, the processes of citric acid sorption on basic yttrium carbonate and transformation of amorphous yttrium carbonate hydroxide into crystalline yttrium hydroxide occurs. It is only after 72 h of synthesis that the crystalline yttrium citrate dihydrate is formed.•Synthesis crystalline yttrium citrate dehydrate.•The synthesis time 72 h.•Synthesis components: the freshly precipitated basic yttrium carbonate phase in a citric acid solution.

STUDY OF THE EFFECT OF THE BUFFER LAYER ON THE SUBSTRATE SURFACE AND THE PROCESS MEDIUM ON NANOCLUSTER FORMATION IN THE Si1 – xGex STRUCTURE

In this paper, we report the experimental results of the effect of the initial buffer layer on the substrate surface and the process medium on the possibility and features of the formation of Si1 – xGex nanoclusters (Si, Ge, and SiGe). We proposed a mechanism for the formation of silicon, germanium, and silicon–germanium nanoclusters on buffer layers of amorphous silicon, silicon nitride, and silicon, dysprosium, and yttrium oxides. The effect of the initial buffer layer on the substrate surface under the film deposition conditions of nanostructured silicon doped with germanium (NSS(Ge)) on the configuration, size, and surface concentration of nanocrystals is shown.

Cathodoluminescence and microstructural analysis of amorphous yttrium-aluminum-borate luminescent powders

We present the cathodoluminescence (CL) and microstructural analysis of amorphous yttrium aluminum/aluminium borate (a-YAB) luminescent powders synthesized by polymeric precursor (PP) and sol-gel (SG) based wet-chemical methods. The a-YAB powders exhibit bright photoluminescence tunable from intense blue to white chromaticity region depending on their calcination temperature. Here, the influence of calcination temperature on CL and microstructural properties of the a-YAB powders has been investigated. The a-YAB powders showed weak but homogeneous CL. Within the optimum calcination temperatures for photoluminescence (650–740 °C for PP and 450–600 °C for SG series), the CL observed to be more intense for powders synthesized at higher calcination temperature. The microstructure analysis revealed that the SG series powders calcined below 570 °C exhibit intraparticle chemical inhomogeneity, whereas no such inhomogeneity could be seen in PP series powders, owing to their higher calcination temperatures. Nevertheless, both series exhibit similar luminescence broadening with calcination temperatures despite these microscopic differences, revealing that the luminescence broadening does not depend on the chemical properties at the microscopic level, but is controlled by more intrinsic effects on the luminescent centers or its immediate surrounding as a function of calcination temperature.

Impact of Schottky junctions in the transformation of switching modes in amorphous Y2O3-based memristive system

In this report, we study factors that dominate the mode transformation of resistive switching (RS) in yttria based memristive devices. It is found that amorphous yttria films are more suitable for RS whereas highly crystalline films are counterproductive for RS. The transformation from unipolar to bipolar resistive switching mode is demonstrated in our devices via moving from a system of single Schottky barrier diode (SBD) to double SBD. The conduction mechanism behind these transformation mechanisms is found to be predominantly interfacial. We also report a forming-free Al/Y2O3/Al based memristor fabricated by the dual ion beam sputtering without any post-processing steps for the first time. It shows stable switching behavior for >29 000 cycles with good retention (105 s) characteristics.

The effect of zirconia substitution on the high-temperature transformation of the monoclinic-prime phase in yttrium tantalate

Amorphous yttrium tantalate, as well as solid solutions containing zirconia, transform on heating to a monoclinic-prime phase and then, with further heating, to a crystalline tetragonal (T) solid solution phase at ∼1450 °C. On subsequent cooling the tetragonal phase converts by a second-order displacive transformation to a different monoclinic phase not to the monoclinic-prime phase. On subsequent reheating and cooling, the phase transformation occurs between the monoclinic (M) and tetragonal phases, and the monoclinic-prime phase cannot be recovered. The limit of zirconia solubility in both the monoclinic-prime and monoclinic phases lies between 25 and 28 m/o ZrO2, consistent with previous first-principles calculations. The monoclinic-prime phase is stable up to at least 1400 °C for 100 h for zirconia concentrations from 0 to ∼60 m/o ZrO2. This temperature exceeds the temperature of the equilibrium M-T phase transformation suggesting that the monoclinic-prime phase transforms directly to the tetragonal phase by a reconstructive transformation and is unaffected by the zirconia in solid solution.

Growth of Y3Fe5O12 films on Si with AlO x and SiO2 buffer layers by ion beam sputtering

Amorphous yttrium iron garnet films ranging in thickness from 100 to 600 nm have been produced on single-crystal silicon substrates by sputtering a polycrystalline target with the composition Y3Fe5O12 (yttrium iron garnet) by a mixture of argon and oxygen ions. Before film growth, AlO x or SiO2 buffer layers up to 0.8 μm in thickness were grown on the Si surface. The heterostructures were crystallized by annealing in air at a temperature of 950°C for 30 min. The properties of the films were studied by magneto-optical techniques, using Kerr effect and ferromagnetic resonance measurements. The Gilbert damping parameter reached 2.8 × 10–3 and the effective planar magnetic anisotropy field was independent of the nature of the buffer layer. This suggests that the thin-film heterostructures obtained in this study are potentially attractive for use in spin-wave semiconductor devices.

Annealing of amorphous yttrium iron garnet thin films in argon atmosphere

We report the recrystallization of amorphous Yttrium Iron Garnet (YIG) thin films by annealing in an argon atmosphere. Our results show that the amorphous film transforms into a fully epitaxial layer. Compared to annealing in oxygen, the argon atmosphere has no significantly deteriorating influence on the structural and magnetic properties of the YIG thin films. In ferromagnetic resonance experiments, low damping and narrow linewidth can be obtained. For a 65 nm thick layer, a damping constant of α = (1.61 ± 0.25) × 10–4 is found and the linewidth at 9.6 GHz is as small as 2.26 ± 0.10 Oe. These values are comparable to the best results for YIG thin films grown at high temperature pulsed laser deposition and almost as good as for thin YIG films deposited at room temperature and annealed in oxygen. Annealing in vacuum or growth in argon atmosphere, however, results in non-magnetic material.

The enhancement of fracture toughness and tribological properties of the titanium nitride films by doping yttrium

In this paper, yttrium was incorporated into titanium nitride matrix to deposit TiYON films using a reactive magnetron sputtering system and the microstructure, mechanical and tribological properties were investigated. The results showed that solid solution face centered cubic (fcc) TiYN was the major phase of the film when the yttrium content was <7.8at.%. When the yttrium content was further increased, the film exhibited mixed phases of fcc-TiYN and amorphous yttrium oxide, this induced grain refinement and appearance of lots of grain boundaries. Hardness of the films first rose from 21GPa at 0at.% Y to 26GPa at 10.2at.% Y, and remained stable as the yttrium content was above 10.2at.%. The hardness was influenced by the amorphous yttrium oxide phase, solid solution strengthening, grain boundaries and residual stress. Between 0at.% to 7.8at.% of yttrium, the fracture toughness (KIC) rose slowly, KIC rose sharply to 0.85MPa.m1/2 as the yttrium content was 10.2at.% due to the formation of amorphous yttrium oxide phase, it rose slowly again with a further increase in yttrium content. For the film at <7.8at.% Y, average friction coefficient (μ) and wear rate were influenced by the load significantly and there was an obvious rise in their values with an increase in load. A further increase in yttrium content in the films, improved the tribological properties, μ and wear rate were almost independent on the load. Fracture toughness enhancement attributed to the improved load capacity and tribological properties.

Fabrication of Fe-base superalloy powders with yttrium oxide dispersion by mechanical alloying and chemical route

The ferritic alloy powders with homogeneous dispersion of yttrium oxide nanoparticles were fabricated by polymeric additive solution route. The Fe-Cr-Al-Ti alloy powders were prepared by high energy ball milling, and yttrium oxide particles on the alloyed powder surfaces were formed by calcination of a precursor solution containing yttrium nitrate and polyvinyl alcohol. In the powder mixture calcined at 600°C, amorphous yttrium nanoparticles were formed, whereas homogeneous ferric ODS alloy powders with dispersion of Y4Al2O9 crystal nanoparticles were observed by the chelating reaction between yttrium cations and PVA in the powder mixture after calcination at 800°C. This study contributes a promising approach to fabricate ferritic ODS alloys with homogeneous dispersion of oxide nanoparticles.

Synthesis of Carbon‐Supported Pt–YOx and PtY Nanoparticles with High Catalytic Activity for the Oxygen Reduction Reaction Using a Microwave‐based Polyol Method

AbstractCarbon‐supported PtY alloy nanoparticles were prepared as oxygen reduction reaction (ORR) catalysts by reducing a mixture of cis‐[Pt(NH3)2(NO2)2] or Pt(C5H7O2)2 and Y(CH3COO)3⋅4 H2O in ethylene glycol (EG) with microwave (MW) heating. Microstructure and composition analyses of products by using TEM, TEM–energy‐dispersive X‐ray spectroscopy (EDS), XRD, X‐ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP‐AES) data showed that Pt–YOx/C (Y/Pt=0.11–0.75) catalysts involving amorphous yttrium oxide were formed as major products. When the YOx component in the catalysts was removed by using HNO3 treatment, Pt99.1–99.6Y0.4–0.9/C alloy catalysts with low Y contents remained. Higher ORR activity was shown by Pt–YOx/C and PtY/C catalysts than by Pt–Y(OH)3/C, Pt–YOx/C, or PtY/C catalysts prepared by using other conventional chemical reduction methods and thermal treatment methods under a H2/Ar or Ar atmosphere. The mass activity (MA) and surface specific activity (SA) of the best Pt99.5Y0.5/C catalyst, MA=245 A gPt−1 and SA=711 μA cmPt−2, were equal to or higher than those of the commercially used Pt86Co14/C catalyst, MA=245 A gPt−1 and SA=512 μA cmPt−2. The major reasons for the high ORR activity of these Pt–YOx/C and PtY catalysts are discussed. These Pt99.1–99.6Y0.4–0.9/C alloy catalysts prepared by using acid treatment are new and promising catalysts for use in proton exchange membrane fuel cells (PEMFCs).

Magnetic and magnetocaloric properties of amorphous Y3Fe5O12 compound

We report a theoretical model formed by two coupled magnetic sublattices of localized spins in the presence of an applied magnetic field to investigate the magnetic characteristics and magnetocaloric properties of amorphous yttrium iron garnet. The magnetic state equation is based on Handrich–Kobe´s theory, where the amorphization is taken into account by introducing fluctuations in the exchange parameters. Experimental results report that Y3Fe5O12 presents a structural phase transition from crystalline to amorphous caused by a variation of external pressure. This phase transition on Y3Fe5O12 leads to interesting results in the magnetic properties and magnetocaloric quantities.

Nondestructive Encapsulation of CdSe/CdS Quantum Dots in an Inorganic Matrix by Pulsed Laser Deposition.

We report the successful encapsulation of colloidal quantum dots in an inorganic matrix by pulsed laser deposition. Our technique is nondestructive and thus permits the incorporation of CdSe/CdS core/shell colloidal quantum dots in an amorphous yttrium oxide matrix (Y2O3) under full preservation of the advantageous optical properties of the nanocrystals. We find that controlling the kinetic energy of the matrix precursors by means of the oxygen pressure in the deposition chamber facilitates the survival of the encapsulated species, whose well-conserved optical properties such as emission intensity, luminescence spectrum, fluorescence lifetime, and efficiency as single-photon emitters we document in detail. Our method can be extended to different types of nanoemitters (e.g., nanorods, dots-in-rods, nanoplatelets) as well as to other matrices (oxides, semiconductors, metals), opening up new vistas for the realization of fully inorganic multilayered active devices based on colloidal nano-objects.

Solution-Derived Amorphous Yttrium Gallium Oxide Thin Films for Liquid Crystal Alignment Layers

Solution-Derived Amorphous Yttrium Gallium Oxide Thin Films for Liquid Crystal Alignment Layers