Polycrystalline Compounds Research Articles

Multiferrocity in spin chain based polycrystalline Sm2BaCoO5

Sm2BaCoO5, a spin chain based polycrystalline compound which crystallize in orthorhombic structure (space group, Immm), is known to order antiferromagnetically close to 38 K. As motivated by 1) its Tb analogues [1] which show giant magneto-dielectric coupling and a new type-II multiferroic and 2) recently discovered multiferroicity in Sm2BaMO5 (M=Ni and Cu) compounds [2,3], detailed dielectric, ferroelectric and magneto-electric measurements have been carried out for Sm2BaCoO5. Magnetic and heat capacity measurements confirm the antiferromagnetic ordering at around 38 K. Interestingly ferroelectric transition also occurs around 38 K as revealed by frequency independent dielectric data as well as pyro-current measurements in various protocols. Therefore, the presented experimental results show that spin chain oxide Sm2BaCoO5 is new type-II multiferroic and we have identified R2BaCoO5 (R=Tb, Sm)- spin chain based cobaltates, is the new multiferroic series, so far unexplored.

Photoluminescent Lanthanide(III) Complexes Based on 2-[((4-Chlorophenyl)amino)methylene]-5,5-dimethylcyclohexane-1,3-dione

Five coordination compounds of the general formula [LnL2(NO3)3]n (Ln3+ = Eu (I), Sm (II), Tb(III), Dy (IV), and Gd (V)) are synthesized from 2-[((4-chlorophenyl)amino)methylene]-5,5-dimethylcyclohexane-1,3-dione (L). The crystal structures of the ligand and complex III are determined by X-ray diffraction (XRD) of single crystals (CIF files CCDC nos. 2298715 (L) and 2298716 (III)). Complex III is polymeric due to the bidentate-bridging coordination of the ligand by the oxygen atoms of the cyclohexanedione fragment, and the coordination number of the central atom is ten. According to the phase XRD data, all synthesized polycrystalline compounds are isostructural to the single crystals of complex III. The photoluminescence properties of the ligand and coordination compounds in the polycrystalline state are studied. The energy transfer from the ligand to lanthanide(III) ion is shown to proceed via the “antenna” mechanism in the case of the europium(III), samarium(III), and terbium(III) compounds. Among the series of the complexes, the highest quantum yield is observed for compound I (21.9%), and the sensibilization efficiency of the europium(III) complex is 43.5%.

Near-room-temperature magnetic properties and magnetocaloric effect of polycrystalline and nano-scale manganites Pr(0.65-x)NdxSr0.35MnO3 (x ≤ 0.35)

Here we report investigations of structural, electrical and magnetic properties of bulk and nano-sized Pr0.65-xNdxSr0.35MnO3 compounds (x ≤ 0.35). Polycrystalline compounds were produced by solid – state reaction and nanocrystalline samples were obtained by sol–gel method. Analysis of x-ray diffraction patterns revealed a change in lattice structure from ‘Pbnm’ to ‘R3c’ symmetry, with diminishing cell volume upon increasing Nd ions substitution for all samples. Optical microscopy was used for bulk surface morphology and transmission electron microscopy was implemented for nano-sized samples. Iodometric titration showed oxygen deficiency for bulk compounds and oxygen excess for nano-sized particles. Measurements of resistivity of bulk samples revealed a single peak at temperatures associated with grain boundary conditions and with ferromagnetic/paramagnetic transition and negative magnetoresistivity. Critical magnetic behavior analysis disclosed that the polycrystalline samples are governed by a tricritical mean field and by 3D Heisenberg models while nanocrystalline samples are governed by a mean field model. Curie temperature Tc values remain in near room temperature range for all bulk compounds; they lower with increasing Nd ions substitution from 295 K for the parent bulk compound to 268 K for x = 0.35. Tc is lowered from 255 K for the parent nano-sized compound in small temperature intervals. All compounds exhibit second-order magnetic phase transitions and relatively high magnetic entropy change, with the highest value of 5.74 J/kgK for x = 0.25 bulk sample in μ˳∆H = 4 T. Strong magnetocaloric effect, stability and the possibility of fine-tuning Tc by Nd ions substitution make the investigated bulk polycrystalline compounds promising for application in magnetic refrigeration. Nano-sized samples possess lower magnetic entropy changes of maximum 2.4 J/kgK in μ˳∆H = 4 T for x = 0.15, but wider effective entropy change temperature (δTfwhm) and relative cooling power on par with other manganites, bringing them into the conversation as a viable option in cooling materials.

Outstanding Room‐Temperature Thermoelectric Performance of n‐type Mg3Bi2‐Based Compounds Through Synergistically Combined Band Engineering Approaches

AbstractThermoelectric cooling materials based on Bi2Te3 have a long history of unsurpassed performance near room temperature. Recently, research into price‐competitive Mg3(Bi, Sb)2‐based materials are focused on replacing traditional cooling materials. Here, the thermoelectric properties of Mg3.2Bi1.998−xSbxTe0.002Cu0.005 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) polycrystalline compounds are investigated. In all temperature regions, electrical resistivity and Seebeck coefficient are increased with Sb concentration. The electronic transport properties of Sb‐alloyed compounds are maximized by synergistically combined band engineering approaches such as band structure change caused by lattice strain, increased electronic density of states, and chemical potential shift, leading to exceptionally high‐power factor values of over 3.0 mW m−1 K−2 at room temperature. Furthermore, with increasing Sb content, thermal conductivity values are systematically reduced due to the promotion of alloy scattering of phonons and suppression of the bipolar contribution. Consequently, these multiple approaches significantly enhance thermoelectric performance, resulting in an enhancement of thermoelectric figure‐of‐merit zT above 1.1 at 348–423 K. Additionally, a zTavg of 1.1 is recorded at 300–450 K, making it an unrivaled value among the reported n‐type Mg3Bi2‐based thermoelectric materials. Overall, this work demonstrates that Mg3Bi2‐based materials are more promising for thermoelectric cooling applications compared to Bi2Te3‐based materials.

Enhancement of the magnetocaloric properties of a composite based on Pr0.5Sr0.5MnO3 and Pr0.4Gd0.1Sr0.5MnO3 compounds

In the present study, we investigate the magnetocaloric properties of Pr0.5Sr0.5MnO3 and Pr0.4Gd0.1Sr0.5MnO3 polycrystalline compounds, which were elaborated via the solid-state reaction method, to prepare a composite with a high relative cooling power (RCP). Theoretical calculations were used to predict the proportions of the selected sample. Our composite was found to be active over a very wide temperature range and is characterized by an improvement in the RCP. The obtained results allow us to conclude that our compound may be a promising candidate for magnetic refrigeration. In addition, the critical behavior of our selected sample was studied, and the critical exponents were determined. All results were discussed.

Large magnetocaloric effect and giant magnetoresistance in rare earth based intermetallic compound ErAl3: construction of magnetic phase diagram

This study explores the magnetic and magnetotransport behavior of polycrystalline ErAl3 compound. The polycrystalline compound adopts HoAl3-type structures with the R-3m space group, No. 166-2 and hR60 configurations. Multiple magnetic orderings and two field-induced metamagnetic transitions are observed. ErAl3 exhibits a significant magnetocaloric effect (MCE), −ΔSM = 15.25 J kg−1 K−1 and high relative cooling power of 383 J kg−1 with applied magnetic field change (ΔH) of 70 kOe near the paramagnetic to ferromagnetic transition, showcasing its potential for magnetic refrigeration technology. The compound also demonstrates metallic behavior, with a notable magnetoresistance of 48.5 % at 2 K due to the suppression of antiferromagnetism. The magnetic phase diagram reveals four distinct phases influenced by temperature and magnetic field, identified through the study of the MCE.

Narrowing of band gap and decrease in dielectric loss in La1-xSrxMnO3 for x = 0.0, 0.1, and 0.2 manganite nanoparticles

Polycrystalline compounds of lanthanum strontium manganite (La1-xSrxMnO3, LSMO) are widely used in electronic storage devices due to their minimal losses and electronic charge transport properties. In this study, we investigated how varying substitutions of Sr2+ for values of x = 0.0, 0.1, and 0.2 affected the tuning of the optical band gap and dielectric losses in La1-xSrxMnO3 nanoparticles. Synthesized samples were structurally analyzed via X-ray diffraction. A rhombohedral R3¯c crystal structure was confirmed for all prepared samples; crystallite size ranging from 15 nm to 20 nm was estimated along with other lattice parameters. Polygonal or hexagonal-like morphology was revealed by field emission scanning electron microscopy, with a moderate size distribution of nanoparticles affected by thinner grain boundaries in doped LSMO. Energy dispersive spectroscopy was employed to confirm the elemental composition of each compound, and the infrared spectrum indicated bonding in the fingerprint region It was observed that there was a significant reduction in the optical band gap, which was measured using ultraviolet spectrometer absorption data. The band gap decreased from 4.34 eV to 4.11 eV. This reduction was found to be related to the difference in refractive index, which was calculated using both Moss and Herve–Vandamme relations. In parallel, frequency-dependent dielectric analysis revealed that frequency was proportional to the increase in Sr content, inversely affecting dielectric loss. Moreover, the AC conductivity of the prepared samples increased with the rise in Sr content, as described by Johnscher’s universal power law in the region of high frequency.

Effect of Partial Doping with La Atoms on Some Superconducting and Electrotransport Characteristics of Y1-x LaxBa2Cu3Oy Polycrystals

The effect of the location with different concentrations of La atoms (x = 0; 0.02; 0.028; 0.11) on some superconducting and electrotransport characteristics of Y1−xLaxBa2Cu3Oy polycrystalline compounds was studied by recording the temperature dependence ρ(T) curves of resistivity in the case of direct current in the range of temperatures (77K - 300K). The temperatures at the onset (Τcon) and offset (Tc0) of the transition, as well as the width of the transition - ΔΤc = Τcon-Tc0, were considered as the superconducting characteristics. The absolute values of ρ(300K) and ρ(100K) and their ratio a = ρ(300K)/ρ(100K) were considered as electric transport characteristics, as well as the temperature coefficient of resistivity dρ/dT, which was determined by ρ(T) in the range of linear dependence with the slope of the curve. From the comparison of these characteristics, it was concluded that there is a certain correlation between the superconducting and electrotransport properties of the studied compounds depending on the concentration x of the partial location of Y atoms with La. Type:

Spin-phonon coupling driven magnetodielectric effect in low-dimensional complex magnetic BaGdFeO4 system

In this report, we have investigated the detailed magnetodielectric properties associated with spin-phonon coupling in the BaGdFeO4 polycrystalline compound, X-ray diffraction study confirms the orthorhombic crystal structure with a space group of Pnma. The DC magnetization measurements indicate the complex magnetic behavior with multiple magnetic transitions at TN1 = 62 K and TN2 = 31 K. In the field-dependent magnetization study, field-induced metamagnetic transitions and their temperature dependence have been attributed to the competing magnetic interactions of two magnetic sub-lattices with rare-earth (Gd3+) and Fe3+ magnetic spins. Dielectric measurements have revealed the correlation of observed dielectric anomalies with the magnetic transitions. The frequency-independent and magnetic field-dependent dielectric anomalies, along with the corresponding magnetic transitions, thus corroborate the subtle magnetodielectric coupling studied by temperature-dependent magnetodielectric measurements. We discuss possible origins for the magnetodielectric behavior in terms of weak spin-phonon interactions, as confirmed by the temperature-dependent Raman spectra measurements.

Deep insights into morphological, structural and dielectric properties of BaTi0.5 (Cr0.33Mo0.17) O3 ceramics

In our present paper, the morphological, structural and electrical properties of chromium-doped BaTiO3 ceramics were investigated. BaTi0.5 (Cr0.33 Mo0.17)O3 was prepared by the sol-gel technique. Tetragonal phase with P4mm space group was observed by X-ray diffraction analysis. An excellent agreement between the calculated and the observed model was verified by Rietveld refinement. A polycrystalline compound with a particle size of 1.96 μm was identified using scanning electron microscopy. The electrical conductivity graph is divided into two regions in the frequency interval 102–106 Hz over the temperature range 480–640 K. The Ac conductivity spectrum follows the Jonscher's law. The conductivity mechanism in the studied temperature range can be explained by the Non-overlapping Small Polaron Tunnel (NSPT) model. The imaginary parts of impedance show that the maximum value of Z″ decrease with temperature rise, reflecting the progressive loss of insulating properties. In addition, the peaks of Z″ shifted to higher frequencies, indicating relaxation behaviour. Furthermore, the real part of Z″ decreased with temperature and frequency increase, indicating Negative Temperature Coefficient Resistance (NTCR) behaviour. The complex impedance plot showed large semicircular arcs corresponding to the merging of two semicircles due to grain and grain boundary contribution. Examination of the impedance and modulus normalization curves revealed a shift in both peaks, indicating the existence of a short moving carrier. The exponent “n" increased with temperature increase, which proves the existence of the Non-overlapping Small Polaron Tunnel (NSPT) model in the studied temperature range.

Elastic, electronic, and magnetic properties of MNb2O6 (M = Mn, Fe, Co, Ni) in the orthorhombic Pbcn structure, a computational study

The orthorhombic niobates containing magnetic transition ions such as Mn, Fe, Co, and Ni show excellent promise for materials in energy storage, electro-photoactivity, and low-dimensional magnetic character. We report on the computational studies focusing on the elastic, electronic, and magnetic properties of four compounds with chemical formulae MNb2O6 (M = Mn, Fe, Co, Ni) in orthorhombic Pbcn crystal structure using the plane wave density functional theory (DFT) computations. The fully optimized crystal structures were used to study the elastic stiffness, compliance, bulk, and young moduli, the Poisson ratios, and anisotropy constants in both single crystal and polycrystalline compounds. Moreover, the electronic structure including the bandgaps, density of states, and magnetic states was also determined. The bandgap values of 2.98 eV, 2.64 eV, 2.70 eV, and 1.86 eV were obtained for MNb2O6 (M = Mn, Fe, Co, Ni), respectively. The Young’s modulus in all samples showed anisotropic behavior. The sound velocity and Debye’s temperature showed a decrease across the series MNb2O6 (M = Mn, Fe, Co, Ni). All four compounds have an antiferromagnetic ground state and the spin-only moments of these ions were found to be 4.55 μB for Mn3+, 3.62 μB for Fe3+, 2.64 μB for Co3+, and 1.68 μB for Ni3+. Overall, this study provides a comprehensive theoretical investigation of the basic materials properties of MNb2O6 (M = Mn, Fe, Co, Ni) which will enable the researcher working on the application of these materials in devices to carefully tailor their properties according to the application requirements.

Room temperature ferromagnetism, optical band gap widening in Mg-doped ZnO compounds for spintronics applications

In the present research work, a conventional solid-state synthesis approach was used to synthesize the polycrystalline compound of Mg-doped ZnO (Zn1-xMgxO with x = 0–0.12). The XRD analysis reveals that Mg-doped compounds have been crystallized in a single hexagonal phase. The SEM analysis revealed that these compounds are constituted with microscopic spherical particles with a size range of 1–3 μm. Raman scattering spectra of these compounds displayed a blue-shift of the Raman active E2 (low) mode attributed to the vibration of zinc atom in wurtzite ZnO, indicating Mg ions were substituted successfully into the ZnO lattice. Optical measurements revealed that the optical band gap enhanced from 3.12 to 3.17 eV, while the transmittance value improved from 87% to 96% as the Mg doping percentage is increased. The magnetization (M) versus applied field (H) measurements, done at 300 K reveals that the undoped ZnO compound exhibits weak ferromagnetic behavior, whereas all Mg-doped ZnO compounds show a strong ferromagnetism with coercivity ranging between 85Oe≤Hc≤1482Oe, and with the highest saturation magnetization of 0.255 emu/gm for 12% Mg-doped sample.

Oxidation in Ca/K-1144 iron-based superconductors polycrystalline compounds

Iron-based superconductors (IBSCs) are a class of material under investigation for the development of superconducting wires in the low-temperature-high magnetic fields power application. Among the various families of IBSCs, the 1144 CaKFe4As4 compound is a promising material able to achieve outstanding superconducting properties with a cheap and simple chemical composition. Oxidation, in these compounds, is considered an obstacle for high intergranular critical current density, Jc,GB. A study devoted to the evaluation of oxidation phenomena and their effects on the superconducting properties is thus needed in order to fully understand the involved mechanisms. From the evaluation of polycrystalline samples obtained by a mechanochemically assisted synthesis route, a degradation of the critical temperature and critical currents has been observed concurrently with oxygen accumulation at grain boundaries in open porosities. However, the crystalline structure at an atomic level seems not affected, as well as intragranular superconducting properties assessed by means of calorimetric methods. These results suggest that loss of superconducting properties in Ca/K-1144 compounds following oxidation is significantly associated with the worsening of grain connectivity.

Synthesis and characterization of a new ordered rhombohedral pyrochlore family Ln3Sb3Cu2O14 (Ln=Pr,Nd, Sm, Eu, Tb, Dy) with more detailed study of the Sm compound

New polycrystalline compound with a rhombohedral pyrochlore structure and chemical formula Sm3Sb3Cu2O14 was synthesized in air by solid-state reaction method. The compound crystallizes in the rhombohedral system, with R-3m space group and Z = 3. Lattice parameters are a = 7.41681(2) Å and c = 17.24845(5) Å. The electrical resistivity, measured by impedance spectroscopy, highlights a semiconductor behavior with an activation energy Ea = 0.47 eV. The dielectric properties show a regular decrease of permittivity with temperature, the dielectric loss decreases at low temperature and remain stable around 0.8 at high temperature. Using UV–vis Diffuse Reflectance, we can assume that the band gap is around 3.28 eV. The magnetic susceptibility of Sm3Sb3Cu2O14, measured from 5 K to 800 K, shows Curie-Weiss paramagnetism behavior with a significant Van Vleck contribution from the Sm+3 magnetic cation.

Mueller-matrix imaging polarimetry elevated by wavelet decomposition and polarization-singular processing for analysis of specific cancerous tissue pathology.

Mueller-matrix polarimetry is a powerful method allowing for the visualization of malformations in biological tissues and quantitative evaluation of alterations associated with the progression of various diseases. This approach, in fact, is limited in observation of spatial localization and scale-selective changes in the poly-crystalline compound of tissue samples. We aimed to improve the Mueller-matrix polarimetry approach by implementing the wavelet decomposition accompanied with the polarization-singular processing for express differential diagnosis of local changes in the poly-crystalline structure of tissue samples with various pathology. Mueller-matrix maps obtained experimentally in transmitted mode are processed utilizing a combination of a topological singular polarization approach and scale-selective wavelet analysis for quantitative assessment of the adenoma and carcinoma histological sections of the prostate tissues. A relationship between the characteristic values of the Mueller-matrix elements and singular states of linear and circular polarization is established within the framework of the phase anisotropy phenomenological model in terms of linear birefringence. A robust method for expedited (up to ) polarimetric-based differential diagnosis of local variations in the poly-crystalline structure of tissue samples containing various pathology abnormalities is introduced. The benign and malignant states of the prostate tissue are identified and assessed quantitatively with a superior accuracy provided by the developed Mueller-matrix polarimetry approach.

Luminescence and Scintillation Characterization of Sodium-Based Tungstate (Na2W2O7) Crystal for Dark Matter Search

A Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> single crystal was grown with a conventional Czochralski technique in a platinum crucible. A solid-state reaction method was used for the preparation of the polycrystalline compound. Temperature-dependent luminescence and scintillation properties of the crystal were studied under the excitation with a 280 nm UV light-emitting diode (LED) source, an X-ray source, and a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr (beta) source. At different temperatures (from 300 to 10 K), an as-grown crystal’s luminescence and scintillation light output was compared with a CaMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal. Although the light output of Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> crystal at room temperature is lower than CaMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal, at 10 K, it is almost comparable. Compared to room temperature, the crystal’s luminescence and scintillation light output at 10 K were increased by ~17 and ~14 fold, respectively. The decay time of the crystal was studied between 300 to 10 K using a 280 nm LED excitation source, and it varies from 3 (300 K) to ~94 μs (10 K). A thermoluminescence (TL) study was carried out between 10 to 550 K. The kinetic parameters of the TL peaks are calculated with various standard methods. The current result suggests that the studied crystal has good potential as a cryogenic detector for dark matter search experiments in the near future.

Magnetic and Magnetocaloric Properties of Nano- and Polycrystalline Bulk Manganites La0.7Ba(0.3−x)CaxMnO3 (x ≤ 0.25)

Here we report the synthesis and investigation of bulk and nano-sized La0.7Ba0.3−xCaxMnO3 (x = 0, 0.15, 0.2 and 0.25) compounds that are promising candidates for magnetic refrigeration applications. We compare the structural and magnetic properties of bulk and nano-scale polycrystalline La0.7Ba0.3−xCaxMnO3 for potential use in magnetic cooling systems. Solid-state reactions were implemented for bulk materials, while the sol–gel method was used for nano-sized particles. Structurally and morphologically, the samples were investigated by X-ray diffraction (XRD), optical microscopy and transmission electron microscopy (TEM). Oxygen stoichiometry was investigated by iodometry. Bulk compounds exhibit oxygen deficiency, while nano-sized particles show excess oxygen. Critical magnetic behavior was revealed for all samples using the modified Arrott plot (MAP) method and confirmed by the Kouvel–Fisher (KF) method. The bulk polycrystalline compound behavior was better described by the tricritical field model, while the nanocrystalline samples were governed by the mean-field model. Resistivity in bulk material showed a peak at a temperature Tp1 attributed to grain boundary conditions and at Tp2 associated with a Curie temperature of Tc. Parent polycrystalline sample La0.7Ba0.3MnO3 has Tc at 340 K. Substitution of x = 0.15 of Ca brings Tc to 308 K, and x = 0.2 brings it to 279 K. Nanocrystalline samples exhibit a very wide effective temperature range in the magnetocaloric effect, up to 100 K. Bulk compounds exhibit a high and sharp peak in magnetic entropy change, up to 7 J/kgK at 4 T at Tc for x = 0.25. To compare the magnetocaloric performances of the studied compounds, both relative cooling power (RCP) and temperature-averaged entropy change (TEC) figures of merit were used. RCP is comparable for bulk polycrystalline and nano-sized samples of the same substitution level, while TEC shows a large difference between the two systems. The combination of bulk and nanocrystalline materials can contribute to the effectiveness and improvement of magnetocaloric materials.

Orthorhombic YBa2Cu3O7−δ Superconductor with TiO2 Nanoparticle Addition: Crystal Structure, Electric Resistivity, and AC Susceptibility

This article reports the effect of a nanoscale addition of TiO2 on the structure and superconducting parameters of the high-temperature superconductor YBa2Cu3O7-δ (Y123). Polycrystalline compounds of Y123 with different percentages of TiO2, x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were fabricated using the thermal treatment method. An analysis using X-ray diffraction confirmed the formation of Y123 phases for all composite samples. Field-emission scanning electron microscopy (FESEM) analysis revealed the growth of grain size and decrease in porosity, with a sign of partial melting of grains for the samples with TiO2 addition. The magnetic and electric transport properties were investigated using AC susceptibility measurement and the four-probe method, respectively. It was observed that the superconducting transition temperature, Tc-onset, for a pure sample determined by ACS and 4PP was 95.6 K and 95.4 K, respectively. These values were found to decrease with the addition of TiO2, while the superconducting transition (∆Tc) improved with TiO2 addition except for the sample at x = 0.2 wt.%, which showed the broadest transition width. The sharpest superconducting transition (∆Tc) was observed for the sample at x = 1.0 wt.%, indicating that the addition of TiO2 nanoparticles is expected to serve as artificial pinning centres and strengthen the connection among the grains in the Y123 ceramic.

Growth and spectroscopic characterization of Pr:Gd2SrAl2O7 crystal – A potential solid red laser material

In this article, a series of (PrxGd1-x)2SrAl2O7 (x = 0.006–0.05) polycrystalline compounds were synthesized by traditional solid-state reaction to find out the optimum Pr ion’s concentration of the best fluorescence performance for single crystal growth. Then, a transparent 0.95 at.% Pr:Gd2SrAl2O7 (Pr:GSAO) single crystal was successfully grown by the Czochralski method. Spectroscopic properties and Judd-Ofelt theory analysis of this crystal were investigated in detail. The Pr:GSAO crystal has a strong and broad absorption band at about 453 nm, with the absorption cross section of 4.53 × 10−20 cm2 and the full width at half maximum (FWHM) of 5.10 nm (π-polarization), which matches well with the emission bands of InGaN laser diodes. There are a large number of emission peaks in the visible region, the strongest emission peak is located at about 662 nm with the cross section of 1.20 × 10-18 cm2 (π). The fluorescence lifetime of the 3P0 energy level of Pr:GSAO crystal is 5.55 μs. These results reveal that the Pr:GSAO crystal is a potential candidate for red lasers.

Antisite disorder mediated exchange bias effect and spin-glass state in La[formula omitted]Sm[formula omitted]NiMnO[formula omitted

We report the synthesis of La2−xSmxNiMnO6 (x = 0, 0.1, 0.2) polycrystalline compounds through the sol–gel process using all-aqueous precursors. The influence of Sm-substitution on magnetic properties of La2−xSmxNiMnO6 (LSNMO) compounds are investigated through X-ray diffraction (XRD), dc-magnetization (Mdc), ac-magnetic susceptibility measurements, and Raman spectroscopy. XRD analysis confirms that the phase stability of LSNMO is improved significantly upon Sm-substitution as evident from a structural phase transformation of the compound from a biphasic (monoclinic + rhombohedral) into an aphasic (monoclinic) structure. The magnetic measurements indicate a formation of a metastable magnetic state with random ferromagnetic (FM) and antiferromagnetic (AFM) interactions below 100 K. The metastable spin configuration exhibits critical slow-down dynamics and memory effect that signifies a spin-glass (SG) state. The influence of Sm-doping reduces the Curie temperature (Tc) from 284 K → 245 K and enhances saturation magnetization (Ms). These findings are attributed to the combined effect of a reduced degree of antisite disorder upon the addition of Sm. A profound variation (45.5 → 72.9 K) in SG transition temperature (TSG) is also reported. Magnetization loops M(H) confirm the presence of an exchange bias (EB) effect that value suppressed prominently from 120 → 28 Oe upon Sm-substitution. The temperature-dependent magnetization M(T) and frequency-dependent ac-susceptibility χ[ω, T] are used to study the antisite-driven SG phase, spin relaxation dynamics, magnetic memory, and rejuvenation effect. Raman spectroscopy is employed to probe the degree of antisites disorder that reduces after Sm-addition. The phase stability, lower Tc, tunable Ms, and EB in the single-phase compound make LSNMO a potential candidate for its applications in realizing energy-efficient devices.