Ho Concentration Research Articles

Single crystalline Holmium doped InSe for optical limiting operation in Near-IR region

Single crystals possessing nonlinear absorption (NA) character are favorable optical limiter in near infrared region (NIR). The NA features of pure and 0.005%, 0.05%, 0.1% Holmium (Ho) doped single crystals of InSe were analyzed at 1200 nm wavelength within 120 fs and 1 kHz repetition rate. The open-aperture Z-scan technique was employed to determine the NA performance and optical limiting-(OL) threshold. In an attempt to determine the NA coefficients, two types of theoretical models were used. The first model takes into account only the two photon absorption-(TPA), while the second model considers one photon absorption, TPA and free carrier absorption. Based on the experimental results, the main NA mechanism of the studied single crystals is determined as sequential TPA. TPA coefficient value of the pure InSe single crystal increased from 1.41 × 10−10 to 10.7 × 10−10 cm W−1 with increasing Ho doping concentration at 398.1 GW cm−2 input intensity. The NA coefficients increased from 0.84 × 10−9 to 1.62 × 10−9 cm W−1 at the same input intensity. On the other hand, the OL threshold values were found to be 0.027, 0.025, 0.022 and 0.020 J cm−2 at 1200 nm wavelength for pure InSe and the increasing Ho concentration, respectively. The robust NA characteristics and the low OL threshold establish the Ho-doped InSe single crystal as a favorable candidate for OL applications in the NIR spectral region.

Tailoring magnetic properties of novel (La0.25Nd0.25Sm0.25Gd0.25)1-xHoxMnO3 high-entropy perovskite ceramics by Ho doping

High-entropy perovskite ceramics (HEPCs) with equal atomic ratios have recently emerged as a highly promising class of materials due to their unique magnetic properties. However, the crystal structure, microstructure and magnetic properties of unequal atomic ratios HEPCs have yet to be fully investigated. In this paper, single-phase HEPCs (La0.25Nd0.25Sm0.25Gd0.25)1-xHoxMnO3 ((LNSG)1-xHxMO) have been synthesized using solid-state reactions. The effect of Ho element content (x = 0.25, 0.3, 0.35 and 0.4) on the structure and magnetic properties was systematically investigated. All samples exhibit an orthorhombic perovskite structure with a Pbnm space group and show obvious crystallization characteristics after sintering at 1250 °C for 16 h (LNSG)1-xHxMO HEPCs display a smooth surface texture and distinct grain boundaries, as well as significant hysteresis effects at T = 5 K. The spin-orbit interaction and magnetic anisotropy between Ho and Mn ions increase with the increase of Ho content, which increases the saturation magnetization (Ms) of HEPCs. (LNSG)0.6H0.4MO exhibits the lowest magnetic hysteresis losses among the considered samples, attributed to its highest Ms (50.95 emu/g) and the lowest coercivity Hc (0.6 kOe). These characteristics endow it with a potential application in magnetic storage devices.

Effect of Ho content on the microstructural stability and grain growth kinetics of wrought Mg-Y-Ho-Zn alloys

The low microstructural thermal stability of magnesium alloys often leads to a decrease in strength, severely limiting their elevated-temperature applications. In the present work, a microstructure with high thermal stability is developed by rare-earth Ho alloying. The influence of Ho on microstructure evolution and mechanical properties of Mg-Y-Zn alloy during annealing was investigated. The results show that Ho suppresses the generation of W phase (Mg3Zn3Y2) and promotes the precipitation of long-period stacking ordered (LPSO) structure in Mg-Y-Zn-Ho alloys. During the high-temperature applications, the W phase is prone to coarsen, which weakens the pinning effect of grain boundaries, leading to a large grain size. However, after the addition of Ho, the LPSO phase converts to lamella LPSO phases within grains and at grain boundaries. The grain sizes of Mg-Y-Zn-Ho alloys remain stable, which slows down grain growth and stabilizes microstructure. As the content of Ho increases to 2 %, the activation energies of grain boundary migration (GBM) during the grain growth increases from 55 kJ/mol to 103 kJ/mol, indicating that the addition of Ho element hinders grain growth through the formation of lamella LPSO phases. The correlation between the yield strength and grain size of all annealed alloys can be effectively explained by the Hall-Petch (H-P) relationship and LPSO phase refinement.

Impact of Ho substitution on structure, magnetic and electromagnetic properties hard-soft nanocomposites

This work presented the effect of Ho substitution on magnetic and electrodynamic properties of hard-soft SrBaHoxFe12-xO19@NiFe2O4 (x ≤ 0.06) nanocomposites (H/S Ho → SBFeO@NFO NCs) which were produced through one-pot citrate sol–gel method. The structure and morphology were explored using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM). By scrutinizing hysteresis curves at temperatures of 300 K (Room temperature, RT) and 10 K, the magnetic characteristics of H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs have been investigated. These materials display smooth, open hysteresis loops at both temperatures, indicating their ferrimagnetic nature and highlighting the presence of exchange-coupling interactions within the nanocomposites. The SQR (squareness ratio) values, below 0.5 at both high and low temperatures, indicate a multi-domain structure in the H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Magnetic parameters demonstrate fluctuations with growing Ho content. The introduction of Ho3+ ions notably reduce the coercivity of the undoped H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Saturation magnetization (Ms) and magnetic moment show similarity between undoped and Ho-doped nanocomposites at all concentrations, except for x = 0.06, where a considerable decrease occurred at both temperatures. Our findings propose that by controlling the concentration of Ho3+ ions, the magnetic properties of H/S Ho → SBFeO@NFO NCs can be precisely adjusted. Electromagnetic properties of the H/S Ho → SBFeO@NFO NCs were investigated in the range 33–50 GHz. Frequency dispersions of the real/imaginary parts of permittivity and permeability were determined from S11 to S21 parameters. RL coefficient demonstrated intensive electromagnetic absorption with average level −16…−23 dB in this frequency range that corresponded to the absorption of the natural media.

Exploring Ho substituted Y-Fe-B nanocrystalline alloys and hot worked magnets

Aiming to balance the utilization of rare earth (RE) resources and develop Y-Fe-B based permanent magnets, Ho is employed as strategic substitution for enhancing the magnetic properties and thermal stability of nanocrystalline Y-Fe-B alloys. Ho substituting Y can enhance the coercivity of Y-Fe-B alloys while maintaining their excellent thermal stability. 30 at.% Ho substitution leads to an abnormal increase of remanence J r and (Y0.7Ho0.3)2Fe14B alloy exhibits good magnetic properties with remanence J r = 0.73 T, intrinsic coercivity H cj = 303 kA m−1, and maximum energy product (BH)max = 66 kJ m−3. High thermal stability with temperature coefficient of remanence α = −0.124%/K and temperature coefficient of coercivity β = −0.245%/K were obtained between 300–400 K. The results for RE-rich (Y1−xHox)2.5Fe14B alloys also show that the magnetic properties change with Ho content are similar to those of (Y1−xHox)2Fe14B alloys, but the coercivity is higher. In addition, nanocrystalline (Y0.5Ho0.5)2.5Fe14B magnets were prepared by hot-pressing and hot deformation process. Due to the lack of low melting point RE-rich phase, this alloy is difficult to be densified and deformed. The formation of high temperature RE2O3 and RE6Fe23 phases and the lack of continuously distributed RE-rich grain boundary phase are responsible for the poor texture of hot deformed magnet. The hot deformed magnet has the magnetic properties of J r = 0.50 T, H cj = 739 kA m−1, and (BH)max = 40 kJ m−3 together with high thermal stability. The micro-analysis demonstrated the chemical segregation of Y and Ho elements. Higher proportion of Ho than Y existed in main phase and grain boundary phase indicate excess Y were precipitated as Y-rich oxides.

Investigation of structural, electrical, and magnetic variations of Ni-Zn-Co ferrites by substituting rare earth Ho3+ for high-frequency applications

The investigation of structural, magnetic, and electrical properties of Ni0.6Zn0.3Co0.1HoxFe2−xO4 (NZCHF, 0 ≤ x ≤ 0.2) ferrites, synthesized through the sol–gel autocombustion method, has been undertaken. The refined x-ray diffraction (XRD) analysis was performed for XRD data analysis using Fullprof Suite software and it confirmed a single-phase cubic spinel structure, with the determination of crystallite size, refinement parameters and lattice constants. The bulk density of the samples consistently remained lower than the x-ray density, with densities increasing proportionally to the enhancement of Ho concentration. FTIR analysis corroborated the presence of metal-oxygen bonds within the ferrite possessing a spinel cubic structure. 57Fe Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Ho3+ ions that preferentially occupy the B site. The impedance analyzer and vibrating sample magnetometer (VSM) were utilized to measure the real and imaginary parts of the complex permeability and magnetic properties of the samples, respectively. Complex impedance plots were scrutinized to discern the contributions of grain and grain boundary resistances, providing insights into the electrical behavior of the ferrite samples. Furthermore, the introduction of Ho concentration led to alterations in other key properties of the ferrites, including coercivity (H c ), retentivity (M r ), anisotropy constant (K), and magnetic moment (μ B ).The impact of the rare-earth content on the magnetic features of the prepared NiZnCo ferrite microspheres was investigated by analyzing magnetic-hysteresis (M-H) loops, which showed soft ferrimagnetism. Concurrently, the dielectric constant and dielectric loss tangent of the studied samples exhibited a decrease with the rise in Ho3+ concentration. The expected reduction in tan loss in the prepared samples is attributed to the increase in ac resistivity associated with the higher Ho3+ content.

Microstructure, Compressive Properties and Oxidation Behaviors of the Nb-Si-Ti-Cr-Al-Ta-Hf Alloy with Minor Holmium Addition

In the present research, the Nb-Si-Ti-Cr-Al-Ta-Hf alloys with different Ho addition were prepared. Their microstructure, compressive properties and oxidation behaviors were investigated preliminarily. The results exhibit that the Nb-Si-Ti-Cr-Al-Ta-Hf alloy has coarse microstructure which is mainly composed of Nb solid solution, Nb5Si3 and Ti5Si3 phases. The minor Ho addition could refine the microstructure and suppress the precipitation of Ti5Si3 phase. Moreover, the Ho addition also leads to the formation of Ho2Hf2O7, which prefers to precipitate along the Nbss/Nb5Si3 phase interface. Compared with the Nb-Si-Ti-Cr-Al-Ta-Hf alloy, the minor Ho addition improves the room-temperature and high-temperature compressive properties of the alloy. Its room-temperature compressive strength and ductility obtain the maximum value of 1825 MPa and 16.5% when the Ho content is 0.1 at.%. Moreover, its best compressive strength at 873 K, 1273 K and 1473 K is 1495 MPa, 765 MPa and 380 MPa, respectively, when the Ho addition is 0.1 at.%. The oxidation behavior of the Nb-Si-Ti-Cr-Al-Ta-Hf alloy is diversified with the Ho addition. The oxidation rate of the alloy with 0.1 at.% Ho addition is the lowest while the alloy with 0.2 at.% Ho addition is the highest. Therefore, the 0.1 at.% Ho would be the appropriate content for the Nb-Si-Ti-Cr-Al-Ta-Hf alloy.

Synergistic effect and hydrogen migration during co-pyrolysis of oil shale and cherry pit

The pyrolysis oil of oil shale is characterized as being of better quality and having a lower yield, whereas the bio-oil from cherry pit has a higher yield but a higher oxygen content, which limits their efficient and clean application. Thus, the pyrolysates characteristics of oil shale and cherry pit have been investigated using a fixed bed reactor to fully utilize their inherent properties in this paper. In addition, the interaction mechanism during co-pyrolysis is explored by analyzing the hydrogen migration pathways. The results reveal that a remarkable synergistic effect on the oil and gas occurs during co-pyrolysis, and the co-oil yield of OS30CP70 improves by 14.63 % compared with the weighted value. During co-pyrolysis, the concentrations of hydrogen- and oxygen-containing gases are higher than expected, and the hydrogen and oxygen contents of char are lower than expected, which is related to that more hydrogen and oxygen of oil shale and cherry pit migrate into gas instead of char. Additionally, more hydrogen and less oxygen migrate into the co-oil during pyrolysis, causing an increase in aliphatics and a reduction in aromatics and oxygenated compounds, and enhancing the quality of the co-oil. 1H NMR shows that the H· free radical is most likely to attack the Hα and Har sites of cracking fragments rather than Hβ and Hγ sites, resulting in the co-oil containing more short-chain aliphatics and aromatics with fewer rings. Besides, the alkali and alkaline earth metals in cherry pit improve the cracking of hydroxyl and carboxyl groups and inhabit the migration of oxygen into co-oil, leading to a decrease in Ho content. The energy efficiency of co-pyrolysis is higher than that of individual pyrolysis, which all exceed 90 %.

Microwave Absorption Properties of Ceramics Based on BiFeO3 Modified with Ho

Ceramic samples of Bi1−xHoxFeO3, where x = 0.00–0.50, with a modifier concentration variation step ∆x = 0.05–0.10, were prepared by a two-step solid-phase synthesis followed by sintering using conventional ceramic technology. X-ray phase analysis showed that all the solid solutions studied were formed in the presence of impurities. With increasing Ho concentration, a non-monotonic shift in all loss maxima towards the low-frequency region is observed, as well as an increase in their half-width. An increase in the external temperature leads to a monotonic shift in the absorption maxima towards the low-frequency region, which enables the necessary control of the microwave parameters in the X band. A conclusion has been drawn on the feasibility of using the data obtained in the design of new functional materials based on BiFeO3, as well as devices with thermally controlled frequency.

A Self-Powered Broadband Photodetector with High Photocurrent Based on Ferroelectric Thin Film Using Energy Band Structure Design

Self-powered photodetectors have the advantages of high sensitivity, sustainability, and small size and have become a research hotspot in advanced optoelectronic systems. However, the low output photocurrent density seriously hinders the practical application of ferroelectric self-powered photodetectors. Herein, the high-efficiency photoelectric detection performance of the Bi1-xHoxFeO3 ferroelectric self-powered photodetector is realized by doping Ho. The responsivity (R) and detectivity (D*) can reach 0.0159 A/W and 1.94 × 1011 Jones under monochromatic light with a wavelength of 900 nm. Meanwhile, the R and D* can reach 0.022 A/W and 2.65 × 1011 Jones under sunlight. These excellent photodetection performances are attributed to the high short-circuit current density (Jsc). When the Ho content is 6%, the output photocurrent reaches up to 0.81 mA/cm2. The systematic structure and photo-electric characteristic analysis suggest that the decrease in the band gap leads to the generation of a larger photocurrent while the ferroelectric polarization is reduced slightly. This work provides a new way to obtain high-performance self-powered photodetectors.

High-field magnetic and magnetocaloric properties of pseudo-binary Er1−xHoxNi2 (x = 0.25–0.75) solid solutions

Hydrogen is quickly becoming a desired type of fuel, however, the energy and cost required for liquefaction using today’s cooling technology is excessively high. Magnetic cooling based on the magnetocaloric effect is an energy-efficient and environmentally friendly alternative to commonly used vapor compression, but improvements in refrigerants are crucial for this technology to succeed. Polycrystalline Er1−xHoxNi2 (x = 0.25, 0.5, 0.75) Laves-phase solid solutions obtained by the arc-melting method have been investigated due to their potential for low-temperature refrigerants. Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2 crystallize in cubic Laves phase superstructure (space group F-43 m), while Er0.25Ho0.75Ni2, similarly to the initial ErNi2 and HoNi2 binary compounds, crystallizes with the formation of the regular cubic C15 structure (space group Fd-3 m). To evaluate how the structure affects magnetic and magnetocaloric properties, studies in a wide magnetic field range, up to 14 T, were conducted. Measurements show all samples obey the second-order magnetic phase transition from ferromagnetic to paramagnetic state, and their Curie temperatures increase with increasing Ho content from 8 K for Er0.75Ho0.25Ni2 to 12.3 K for Er0.25Ho0.75Ni2. At higher temperatures, all solid solutions are Curie-Weiss paramagnets. However, it has been observed that the formation of the superstructure with lower translational symmetry seems to affect magnetic moments and magnetic entropy values. Er0.25Ho0.75Ni2, with the regular cubic C15 structure, showed the highest entropy changes of 43.5 J/kgK around 12 K, while Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2, with cubic superstructure, provided ∼30 % lower results of 30.3 and 35.1 J/kgK, around 8 and 10 K, respectively, for magnetic field change of 14 T. Nevertheless, relatively large and reversible values of magnetic entropy prove that these compounds can be promising candidates for magnetic cooling operating within the low-temperature range needed for hydrogen liquefaction.

Scheelite trace element compositions: A robust new tool for mineral exploration

Scheelite is a widespread accessory tungstate mineral that contains a variety of trace elements. Scheelites from the major types of magmatic-hydrothermal mineral deposits (86 deposits, including quartz-vein and greisen, porphyry, skarn and orogenic Au deposits) have been collected and analyzed using laser ablation-inductively coupled plasma mass spectrometry (3270 data, including 584 analyses). Discriminant analysis using Mo, Sr, Nb, La, Ce, Eu, Dy, Yb, Y, Ta, Pb, (Ce/Yb)N, (La/Sm)N, (Gd/Yb)N, Eu anomaly, Ce anomaly, (La/Yb)N, LREE/HREE, Y/Ho and Mo + Sr + Nd + rare-earth elements (REE) + Y + Ta + Pb reveals that scheelites from different mineral deposits can be distinguished. Scheelites from quartz-vein and greisen deposits have high total contents of trace elements that partition onto the Ca sites (Mo, Sr, Nd, REE, Y, Ta, Pb). Scheelites from the porphyry W ± Cu ± Mo deposits, which have been studied in this work, are characterized by low Mo and positive Eu than scheelites from porphyry Cu ± Mo deposits. This indicates that large scale tungsten deposits are related to reduced hydrothermal fluids, in contrast to the oxidized fluids associated with porphyry Cu ± Mo deposits. Scheelites from skarn W ± Sn ± Mo deposits typically exhibit a wide range of Y/Ho ratio and a higher sum of the elements Mo, Sr, Nd, REE, Y, Ta, and Pb compared to that from the skarn Cu ± Mo ± W deposits, indicating that increased amount of fluorine probably leads to large-scale W, Mo, and Sn mineralization during magmatic-hydrothermal processes. Scheelites from the greisen W-Sn polymetallic deposits tend to have more restricted Sr compositions and Eu anomalies than those from the quartz vein W-Sn deposits, as well as relatively high Gd, Tb, Dy and Ho contents, which coincide with extensive hydrothermal alteration, indicating intense fluid-rock interaction during mineralization. Using Discriminant projection analysis (DPA), scheelites from many ore deposits can be readily separated from each other. This study demonstrates that heavy-mineral scheelite grains collected during regional geochemical surveys are effective in identifying specific types of buried mineral deposits in potential mineralization area. Scheelite geochemistry with DPA provides an effective guidance for mineral exploration.

Ho-Sb-Te ÜÇLÜ SİSTEMİNDӘ QARŞILIQLI TӘSİRİN Sb2Te3-Ho KӘSİYİ ÜZRӘ TӘDQİQİ

Phase formation in the Sb2Te3-Ho system was studied by methods: differential-thermal (DTA), X-ray phase (XRD), microstructural (MSA), as well as by measuring density and microhardness, and built a T-x phase diagram. It has been established that the phase diagram of the Sb2Te3-Ho system is a non quasi-binary section of the Ho-Sb-Te ternary system. This system intersects the area of the three subordinate triangles of the ternary system. In the system based on Sb2Te3, a solid solution area was found in the range of 0-5 mol% Ho concentration at room temperature.

Effect of Ho Content and Heat Treatment on the Corrosion Resistance of Mg-xHo-3Sm-0.5Zr Alloy

Effect of Ho Content and Heat Treatment on the Corrosion Resistance of Mg-xHo-3Sm-0.5Zr Alloy

Synthesis and characterization of red-emitting Yb/Ho-CaSiO3 upconversion phosphors

Host material plays an important role in obtaining efficient photon upconversion and downshifting luminescence. Generally, fluoride and oxyfluoride glasses-based materials are used for high-efficiency photon upconversion. However, the poor thermal stability of fluoride glasses and the toxicity of fluorine ions limit their applications. In this report, Yb/Ho-doped CaSiO3 wollastonite phosphors have been demonstrated as efficient red-emitting upconversion phosphors. The phosphors have been synthesized by microwave hydrothermal process followed by heat treatment at 1050 ​°C in the air environment. 2M phase of the β-wollastonite has been confirmed by X-ray diffraction and Raman spectroscopy while the existence of the Yb and Ho dopants in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The synthesized samples showed strong red upconversion emission centered at 662 ​nm and near-infrared downshifting emissions at 2016 ​nm upon 980 ​nm excitation. The emissions were found to depend significantly on the Ho concentration. Temporal evolution of the main emission bands was investigated to show that the energy transfer upconversion from Yb to Ho ions was responsible for the efficient upconversion and downshifting phenomenon.

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations.

In most inorganic phosphors, increasing the concentration of activators inevitably causes the concentration quenching effect, resulting in reduced emission intensity at a high level of activator doping and the conventional practice is to limit the activator concentration to avoid the quenching. In contrast, SiAlON ceramics preserve their chemical composition over a very wide range of doping of activator ions, which favors the adjustment and optimization of the luminescence properties avoiding concentration quenching. Here, we investigate the photoluminescence properties of Ho-doped SiAlON (Ho-SiAlON) ceramics phosphors prepared by the hot-press method. Ho-SiAlON ceramics show strong green visible (554 nm) as well as infrared (2046 nm) broadband downshifting emissions under 348 nm excitation. It is shown that there is no concentration quenching, even at a very high level of Ho doping. The emission intensity of the 554 nm band increased two-fold when the Ho concentration is doubled. The results show that the Ho-SiAlON ceramics can be useful for efficient green phosphors.

Phase precipitation and properties of melt-spun Ho-Fe-B alloys prepared by direct quenching and over-quenching followed by heat treatment

Aiming to fully utilize rare earth (RE) resources and develop new high coercivity magnets, the magnetic properties and phase precipitation behavior of Ho-Fe-B alloys were systematically studied. The Ho12+xFe82-xB6 (x = −2, −1, 0, 1, 2) alloys were prepared by melt spinning at various wheel speeds. For the directly quenched Ho12Fe82B6 alloy, the optimum magnetic properties can be obtained at a wheel speed of 22 m/s with the coercivity Hcj = 1.07 × 103 kA/m, remanence Jr = 0.45 T and maximum energy product (BH)max = 36.6 kJ/m3 due to its single Ho2Fe14B phase structure. A maximum Hcj = 2.95 × 103 kA/m can also be obtained at 100 K due to the temperature dependence of anisotropy field and existence of spin reorientation of Ho2Fe14B compound. Jr decreases with decreasing temperature owing to the antiparallel coupling between Ho and Fe moments. The increase of Ho content can enhance the coercivity but deteriorate the remanence. More than 2 at. % reduction of Ho leads to the formation of soft magnetic Ho2Fe17 phase and greatly reduces the coercivity, which is different from many other RE-Fe-B alloys. The phase precipitation behavior of over-quenched amorphous Ho12+xFe82-xB6 alloys during heat treatment were also studied, and the precipitation of Ho2Fe14B phase is confirmed in all alloys. Ho2Fe17 phase precipitates in the Ho10Fe84B6 alloy at the temperature of 882.7 K. The magnetic properties of over-quenched Ho12+xFe82-xB6 alloys after optimally annealed are similar to the directly quenched alloys. In addition, the corrosion resistance of the directly quenched alloys was also investigated. The present results provide reference for developing highly stable RE-Fe-B based magnets with alternative RE resource.

Dielectric, XPS, and ferromagnetic relaxation studies of Ho-substituted polycrystalline magnetic oxide materials

The impact of holmium (Ho) ions on lithium-rich spinel ferrites is studied through magnetic, morphological, and electrical transport properties. The X-ray photoelectron spectroscopy (XPS) analysis indicated the existence of all metal ions in the required valence state. Transmission electron microscopy (TEM) analysis exhibited nano-crystalline (∼50 nm) structures of these ferrites. The electrical resistivity measurements showed the higher resistivity values of the synthesized samples. The resistivity increased from 2.4 × 108 to 2.1 × 1010 Ω-cm with Ho inclusion, indicated an inverse relation with the size of grains. The Curie temperature (Tc) observed to decrease from 848 to 806 K with the incorporation of Ho3+ions. The activation energy (ΔEa) noted to vary between 0.21 and 0.23 eV. The drift mobility (μd) study revealed a decrease from 1.86x10−12to 6.14x10−14cm2V−1s−1by increasing Ho amount up to x = 0.06. A reduction in thermoelectric power (S) from -143 to -95 μ.V/K by increase in Ho concentration confirmed the Fe replacement by Ho on octahedral B-sites. The ferromagnetic resonance (FMR) investigations indicated a drop in FMR line-broadening (ΔH) from 2491 to 2000 Oe by the increase of Ho concentration, making it beneficial to reduce microwave losses. A non-linear variation in the resonance field (Hres) with the substitution of Ho was observed between 7359 to 7785 Oe.

Continuous-wave and pulsed operation of Ho:YLF laser end-pumped by Tm:fiber laser

Continuous-wave and pulsed operation of a Ho:YLF laser was demonstrated. A Tm:fiber laser with 70 W output power was used for the pump source. In this experimental setup, the end-pumped gain medium with 0.5% and 1% Ho concentration in the optical resonators were used. In the continuous-wave regime, 14.2 and 12.8 W linearly polarized power with a concave-concave resonator for 1.0% and 0.5% Ho dopes were extracted, respectively. These amounts correspond to slope efficiencies of 51.9% and 71.3% and optical-to-optical efficiencies of 39.4% and 54.7% for absorbed pump power, respectively. To avoid optical damage, a U-shaped concave-concave resonator was installed, and the resulting spot size in the resonator was about 1.31 mm. The spot size changes about 10% along the total physical length of the resonator. In the pulsed operation regime, for 0.5% Ho concentration with 20 ms pump pulse duration and 10 Hz repetition rates, the free-running output energy was 172 mJ with 16 ms pulse duration. In addition, the absorbed pump energy was about 485 mJ, corresponding to the slope and the optical-to-optical efficiencies of 14.8% and 12.3%, respectively. Also, 27 mJ pulse energy with 29.7 ns duration was achieved for Q-switched operation. Finally, the angle of output beam divergence was measured at approximately 1.1 mrad, and the laser emission wavelength was 2.0568 µm with 0.0065 µm line width.

Role of active slip systems induced with holmium impurity in Bi-2212 ceramics on mechanical design performance and morphological properties

Effect of Ho/Bi partial replacement in Bi2.1-xHoxSr2.0Ca1.1Cu2.0Oy (Bi-2212) superconductors on the fundamental structural, morphological and mechanical performance properties are investigated by Scanning Electron Microscopy (SEM) and Vickers hardness (Hv) measurement techniques. Crystallinity quality and surface morphology including the microcrystal coalescence orientations, grain alignment distributions, microscopic structural problems, microvoids, internal defects, uniform surface view, porosity and particle growth distribution are visually examined with the aid of SEM. Basic mechanical performance and characteristic features of Bi/Ho substituted Bi-2212 superconducting ceramics (0.00 ≤ x ≤ 0.10) are also determined with Vickers tests conducted at various loads intervals 0.245–2.940 N. Experimental findings show that the characteristic features enhance seriously in case of x = 0.01 due to refinement of crystallinity quality and slip systems. Thus, the optimum Ho concentration presents the highest mechanical fracture strength to the load applied as a result of better uniform surface appearance and grain orientations, well-connected flaky layers, larger particle size distribution and denser structure, confirmed by the SEM investigations. Namely, much more load is required to accelerate the dislocation movement and crack propagation to the terminal velocity for critical size growth. The fracture predominantly takes place in the transcrystalline regions and hence the propagations are easily controlled with the optimum Ho dopant ions. On the other hand, the increase in the Ho ions in Bi-2212 structure induces the crack-initiating defects for new stress concentration sites. In conclusion, the permanent and non-recoverable deformations appear at even lower indentation test loads. All samples present indentation size effect feature depending on the dominant character of elastic recovery mechanism. Further, original hardness parameters are semi-empirically analyzed in the plateau limit regions using mechanical modelling approaches for the first time. Based on the analyses, Hays–Kendall model exhibits the closest results to the experimental findings.