Yb Substitution Research Articles

Rational composition engineering toward high thermoelectric performance in p-type EuMg2Sb2-based materials

Mg-based compounds are emerging materials for efficient thermoelectric conversion, as exemplified by n-type Mg3Sb2-based materials, while a high performing p-type Mg3Sb2 material is lacking. EuMg2Sb2, a derivative of Mg3Sb2, has revealed potential as a high-performance alternative to p-type Mg3Sb2-based materials, while pristine EuMg2Sb2 suffers from low carrier concentration. Herein, we reveal that both Zn substitution for Mg and Yb substitution for Eu not only boost the carrier concentration and mobility of p-type EuMg2Sb2-based materials, but also sharply diminish the lattice thermal conductivity via enhancing phonon scattering. Band structure calculation shows that Zn substitution minimizes the energy difference between different bands at the valence band maximum and reduces the band effective mass, leading to optimized band structure. Combined with the role of Ag doping in increasing the carrier concentration and power factor, p-type Eu0.5Yb0.5Mg1.0975Zn0.9975Ag0.005Sb2 sample obtains a maximal dimensionless figure of merit (zT) value of 1.18 at 823 K, which compares favorably to those of EuMg2Sb2 and other p-type Mg–Sb-based Zintl materials. This study demonstrates the efficacy and importance of delicate composition engineering in boosting the thermoelectric performance of p-type EuMg2Sb2.

Yb Substitution and Ultralow Thermal Conductivity of the Ca3–xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) System

A series of Yb-substituted Zintl phases in the Ca3-xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) system has been synthesized by initial arc melting and post-heat treatment, and their isotypic crystal structures were characterized by both powder and single crystal X-ray diffraction analysis. All four title compounds adopted the Ca3AlAs3-type structure (space group Pnma, Pearson code oP28, Z = 4). The overall structure can be described as a combination of the 1-dimensional (1D) infinite chain of ∞1[Al(Sb2Sb2/2)] formed by two vertices sharing [AlSb4] tetrahedral moieties and three Ca2+/Yb2+ mixed sites located in between these 1D chains. The charge balance and the resultant independency of the 1D chains in the title system were explained by the Zintl-Klemm formalism [Ca2+/Yb2+]3[(4b-Al1-)(1b-Sb2-)2(2b-Sb1-)2/2]. A series of DFT calculations proved that (1) the band overlap between the d-orbital states from two types of cations and the p-orbital states from Sb at the high symmetry Γ point implied a heavily doped degenerate semiconducting behavior of the quaternary Ca2YbAlSb3 model and (2) the site preference of Yb for the M1 site was due to the electronic-factor criterion based on the Q values of each atomic site. The electron localization function calculations also proved that the two different shapes of lone pairs of the Sb atoms─the "umbrella-shape" and the "C-shape"─are determined by local geometry and the coordination environment on the anionic frameworks. Thermoelectric measurements of the quaternary title compound Ca2.19(1)Yb0.81AlSb3 showed an approximately two times larger ZT value than that of ternary Ca3AlSb3 at 623 K due to increased electrical conductivity and ultralow thermal conductivity originated from Yb substitution for Ca.

Structural, vibrational and magnetic properties of ytterbium (Yb) and nickel (Ni) substituted BFO particles

In this work, synthesis of Yb and Ni substituted BFO particles have been carried out successfully using sol–gel approach. The particles obtained are of good crystalline nature. With the increasing doping concentration, the crystallite size also has been found to get decreased. It has been observed that for sample x = 0.08 the crystallite size suddenly gets increased. This can be due to the generation of some secondary impurity phase at higher doping concentration. The average crystallite size calculated is about 28.1 nm. The obtained XRD pattern matches perfectly with the standard JCPDS card number 71–2494. A dense morphology of spherical grain size is visible. The sizes of the grains are found to be in the range which is less than 100 nm. Reduction in grain size has been obtained for x = 0.02 samples. Higher surface area for active sites is resulted from reduced grain size. There is availability of 13 Raman active modes. All these modes have rhombohedrally distorted perovskite form and they are within the R3C space group. The value of the spontaneous magnetization (Ms) has been found to be escalating from 0.206 emu/g to 0.789 emu/g, due to doping of Yb and Ni. It has also been observed that, the remnant magnetization (Mr) value has escalated from 0.020 emu/g to 0.052 emu/g due to rise in the doping concentration in the synthesized BYFNO particles. Enhancement in other magnetic parameters like coerciviety and remnant magnetization have also been observed. Incorporation of magnetic Ni ions with Yb substitution can be the major reason for enrichment in the magnetic properties.

Tuning the Intermediate Valence Behavior in the Zintl Compound Yb14ZnSb11 by Incorporation of RE3+ [Yb14-xRExZnSb11 (0.2 ≤ x ≤ 0.7), RE = Sc, Y, La, Lu and Gd

The solid solutions of Yb14-xRExZnSb11 (RE = Sc, Y, La, Lu, and Gd; 0.2 ≤ x ≤ 0.7) were prepared to probe the intermediate valency of Yb in Yb14ZnSb11. The substitution of Yb with RE3+ elements should reduce or remove the intermediate valency of the remaining Yb ions. Large crystals are grown from Sn-flux, and the structure and magnetic susceptibility are presented. All compounds crystallize in the Ca14AlSb11 structure type and the RE3+ ions show Yb site substitution preferences that correlate with size. Two compositions of Yb14-xYxZnSb11 were investigated [x = 0.38(3), 0.45(3)] by temperature-dependent magnetic susceptibility and the broad feature in magnetic susceptibility measurements at 85 K in pristine Yb14ZnSb11 attributed to valence fluctuation decreases and is absent for x = 0.45(3). In compounds with nonmagnetic RE3+ substitutions (Sc, Y, La, and Lu), temperature-dependent magnetic susceptibility shows a transition from intermediate valency fluctuation toward temperature-independent (Y, La, and Lu) or Curie-Weiss behavior and possibly low temperature heavy Fermion behavior (Sc). In the example of the magnetic rare earth substitution, RE = Gd, the Curie-Weiss-dependent magnetic moment of Gd3+ is consistent with x. Hall resistivity of Yb14-xYxZnSb11 showed that the carrier concentration decreases with x and the signature of the low-T intermediate valence state seen for x = 0 is suppressed for x = 0.38 and gone for x = 0.45.

Sol-gel Synthesized Yb-substituted ?-type Hexagonal Ferrites: Study of Structural, Grain Morphology, Electrical Polarization, Electrical Resistivity, Magnetic and Permeability Properties

In present work, an investigation was carried out about the various important properties of Yb 3+ substituted Potassium based ?-hexaferrite KFe 11-x Yb x O 17 (x= 0.0, 0.02, 0.06, 0.1). The Sol-gel auto combustion technique was used to synthesize all the samples. The X-ray diffraction (XRD) patterns confirmed the single hexagonal phase for all prepared samples. The Scanning Electron Microscopy (SEM) confirmed the agglomeration of small particles into big grains. The DC electrical resistivity, measured in the voltage range of (-200V) to (200V), was observed to vary with Yb 3+ contents. The Polarization versus electric field loops revealed the lossy behaviour of pure and substitute samples which indicated the resistive nature of the samples. The saturation and remanence polarization first decreased and then increased with Yb 3+ substitution due to ferric ions distribution between octahedral sites and resistive nature of the samples, respectively. The samples exhibited peculiar magnetic behaviour with the substitution of Yb 3+ ions. The saturation magnetization was increased up to concentration x = 0.06 and then decreased with further substitution of Yb 3+ contents. The coercivity values varied in the range of 141.43 to 279.26 Oe for all the samples which confirmed the soft magnetic nature of present synthesized material. The real part (µ’) and imaginary part (µ’’) of permeability exhibited the high values at low frequencies and these values decreased with the increase of frequency. The prepared samples were supposed to be used as core material of transformer and in high frequency applications due to high resistivity value and low eddy current losses.

Combined Tactics for Elevating the Thermoelectric Performance of CaMg2Sb2‐Based p‐type Materials

Abstractp‐type CaMg2Sb2 has not been favorably considered a promising thermoelectric material in comparison to other Zintl phases. However, a series of meticulously designed tactics is successfully implemented here to analyze and improve the thermoelectric performance of a CaMg2Sb2‐based material. Band structure calculations show that the pristine CaMg2Sb2 has a wide indirect band gap of ≈1.11 eV, which results in its less optimal carrier concentration. To improve its consequently inferior thermoelectric performance, Na doping is first deployed to increase the carrier concentration to an optimal level. Subsequently, the ideal bandwidth and enhanced carrier mobility are simultaneously obtained through Zn alloying. Finally, partial Yb substitution for Ca effectively restrains the bipolar effect in this CaMg2Sb2‐based material and augments its power factor while suppressing its lattice thermal conductivity to a minimum. As a result, a 20‐fold‐higher peak figure of merit (zT) of ≈0.85 at 773 K and an average zT value of ≈0.50 from 298 to 773 K are achieved in Ca0.69Yb0.3Na0.01Mg1.1Zn0.9Sb2, the highest for both values among all [Ca,Mg,Eu,Yb]Mg2Sb2‐based materials reported to date. Furthermore, such a combination of rationally designed tactics as proposed here may assist in exploring the improvement of other thermoelectric materials that have long been overlooked.

Theoretical and experimental investigations: Synergetic effect of Yb–Cu substitution on different properties of hexagonal ferrites

This research project was designed to understand the synergetic effect of trivalent ion Yb3+ and divalent ion Cu2+ co-substitution on different properties of X-type hexagonal nano ferrites. For this purpose, a series of Sr2-xNi2YbXFe28-YCuYO46 X-type hexagonal nano ferrites with concentration (x = 0, 0.02, 0.06, 0.1 & y = 0, 0.1, 0.2, 0.3) was synthesized by adopting the sol gel method. The XRD (X-ray diffraction) results of synthesized samples reveal the formation of single phase for all samples with space group P63/mmc. All the XRD peaks coincided with the reference card (ICDD # 01-073-2034). The theoretical fitting was performed by implementing the Rietveld refinement method to further check the single phase of the samples. The crystallite size and unit cell volume decrease with increasing Yb3+ and Cu2+ contents. The VSM results indicated the hard magnetic nature of all the synthesized materials and theoretically calculated particle size was varied in the range between 9.2 and 11.5 nm. The saturation (Ms) and remanence magnetization (Mr) decreased with the increase in Yb–Cu contents. The value of coercivity (Hc) was first increased and then decreased with the substitutions. Furthermore, the Law of approach to saturation (LAS) was employed to theoretically fit the hysteresis loops. The mixture of spherical and rod shape grains was observed in the SEM micrographs. By adopting the line intercept method, the calculated grain size was varied in the range from 0.691 to 1.33 μm. FTIR spectrum exhibits no extra absorption band due to residual material which also confirms the formation of single hexagonal phase structure. The Thermogravimetric (TGA) analysis divulged the weight losses due to removal of nitrate, vaporization of water molecules and removal of organic compounds at different temperatures. The reflection loss (RL) values have been enhanced with the substitution of Yb–Cu contents.

The impact of Yb substitution on enhancing the thermoelectric properties of CuMnO2 nanostructures

In the present work, CuMn1-xYbxO2 nanostructure with various x values (x ​= ​0, 0.05, 0.1, 0.2) were prepared by high energy ball milling. The structural and morphological properties of the prepared samples were studied by XRD and SEM, analyses. XRD analysis confirms that a pure phase of copper manganese oxide (CuMnO2) was formed till x ​= ​0.05 and the secondary phase of Yb2O3 was observed while increasing the Yb concentration (x ​≥ ​0.1). The SEM images show nano rod-like morphology till x ​= ​0.1 and nanorods were agglomerated in the samples with higher values (x ​> ​0.1). The electrical resistivity and Seebeck coefficient of CuMn1-xYbxO2 (0 ≤ x ​≤ ​0.2) samples were measured at various temperatures. The electrical resistivity of the samples decreased till x ​≤ ​0.1 due to the complete dissolution of Yb ions in CuMnO2 lattice and the resistivity increases at higher Yb substitution (x ​> ​0.2) due to the secondary phase of Yb2O3. The Seebeck coefficient value decreased at x ​= ​0.1 and it increases at a higher x value of 0.2. CuMn0.09Yb0.05O2 shows a higher power factor of 0.0013 ​mW. K−2 m−1 at 575 ​K and low thermal conductivity of 3.2 ​W/m K at 668 ​K which are higher than pure samples. The experimental results show that Yb substitution has an enhanced effect on improving the thermoelectric properties of CuMnO2 nanostructure. The result reveals that the 0.05 ​Yb substituted sample shows a higher figure of merit (ZT) of 2.5x10−4 at 668 ​K.

Magnetic structure and multiferroicity of Sc-substituted hexagonal YbFeO3

The hexagonal rare-earth ferrite $R\mathrm{Fe}{\mathrm{O}}_{3}$ family represents a unique class of multiferroics exhibiting weak ferromagnetism, and a strong coupling between magnetism and structural trimerization is predicted. However, the hexagonal structure for $R\mathrm{Fe}{\mathrm{O}}_{3}$ remains metastable in conventional conditions. We have succeeded in stabilizing the hexagonal structure of polycrystalline $\mathrm{Yb}\mathrm{Fe}{\mathrm{O}}_{3}$ by partial Sc substitution of Yb. Using bulk magnetometry and neutron diffraction, we find that ${\mathrm{Yb}}_{0.42}{\mathrm{Sc}}_{0.58}\mathrm{Fe}{\mathrm{O}}_{3}$ orders into a canted antiferromagnetic state with the N\'eel temperature ${T}_{N}\ensuremath{\sim}165\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, below which the ${\mathrm{Fe}}^{3+}$ moments form the triangular configuration in the $ab$ plane and their in-plane projections are parallel to the [100] axis, consistent with magnetic space group $P{6}_{3}{c}^{\ensuremath{'}}{m}^{\ensuremath{'}}$. It is determined that the spin canting is aligned along the $c$ axis, giving rise to the weak ferromagnetism. Furthermore, the ${\mathrm{Fe}}^{3+}$ moments reorient toward a new direction below reorientation temperature ${T}_{R}\ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, satisfying magnetic subgroup $P{6}_{3}$, while the ${\mathrm{Yb}}^{3+}$ moments order independently and ferrimagnetically along the $c$ axis at the characteristic temperature ${T}_{\mathrm{Yb}}\ensuremath{\sim}15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Interestingly, reproducible modulation of electric polarization induced by magnetic field at low temperature is achieved, suggesting that the delicate structural distortion associated with two-up/one-down buckling of the Yb/Sc planes and tilting of the $\mathrm{Fe}{\mathrm{O}}_{5}$ bipyramids may mediate the coupling between ferroelectric and magnetic orders under magnetic field. The present work represents substantial progress to search for high-temperature multiferroics in hexagonal ferrites and related materials.

Partial cation ordering, relaxor ferroelectricity, and ferrimagnetism in Pb(Fe1 − xYbx)2/3W1/3O3 solid solutions

The structural, magnetic, and dielectric properties of ceramic samples of Yb-doped PbFe2/3W1/3O3 have been investigated by a variety of methods including x-ray powder diffraction, magnetometry, and dielectric spectroscopy. In addition, theoretical investigations were made using first-principles density functional calculations. All the doped samples Pb(Fe1 − xYbx)2/3W1/3O3 (PFYWO) (0.1 ≤ x ≤ 0.5) were found to crystallize in an ordered cubic (Fm3¯m) structure with partial ordering in the B-perovskite sites. Observed changes in the cationic order were accompanied by differences in the dielectric and magnetic responses of the system. While pure PbFe2/3W1/3O3 is antiferromagnetic, the doped Pb(Fe1 − xYbx)2/3W1/3O3 PFYWO samples display excess moments and ferrimagnetic-like behavior, associated with differences in B′ and B″ site occupancies of the magnetic Fe3+ cations. The magnetic transition temperature of the ferrimagnetic phase is found to decrease with increasing Yb content, from TN ∼350 K of the undoped sample down to 137 K for x = 0.5. All PFYWO compounds display a ferroelectric relaxor behavior akin to that of PbFe2/3W1/3O3, albeit our results show significant changes of the frequency and temperature dependence of the dielectric properties. The changes of the properties of PFYWO with increasing Yb substitution can be explained by the changes in the cation size/charge mismatch and the size difference of the two ordered positions.

Sol–gel synthesis of doped Cu2V2O7 fine particles showing giant negative thermal expansion

We report the sol–gel synthesis of Cu2V2O7 fine particles, in which some of the constituent Cu is replaced with other elements. The sintered body of Zn substituted β-Cu1.8Zn0.2V2O7 shows a large negative thermal expansion (NTE) over a wide temperature range due to microstructural effects peculiar to a ceramic body. Using the sol–gel method, we successfully produced β-Cu1.8Zn0.2V2O7 ceramic fine particles that retain the same level of thermal expansion suppression capabilities as the bulk with a size of about 1 μm. We also succeeded in performing rare earth metal (Ce, Sm, Yb) substitutions, which might be a clue for improving NTE performance. These achievements provide particulate filler for thermal expansion control of a micrometer region, which has been earnestly sought in many fields of technology.

Electroluminescence from silicon-based light-emitting device with erbium-doped TiO<sub>2</sub> films: Enhancement effect of ytterbium codoping

In the past years, light-emitting devices (LEDs) based on erbium (Er)-doped insulators or wide-bandgap semiconductors have received intensive attention because the intra-4f transition (<sup>4</sup>I<sub>13/2</sub>→<sup>4</sup>I<sub>15/2</sub>) of Er<sup>3+</sup> ions at ～ 1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth (RE)-doped SiO<i><sub>x</sub></i> (<i>x</i> ≤ 2) or SiN<i><sub>x</sub></i> (<i>x</i> ≤ 4/3) films have been well investigated as the silicon-compatible emitters. However, they suffer difficulty in injecting current and easing fatigue. In this context, the LEDs with RE-doped oxide semiconductors have been extensively investigated out of research interest in recent years. Among the oxide semiconductors, TiO<sub>2</sub> is a desirable host for RE-doping because it is transparent for visible and infrared light, and cost-effective, and has considerably high RE solubility. In our previous work (Zhu C, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 <i>Appl. Phys. Lett.</i> <b>107</b> 131103), we have realized erbium (Er)-related visible and near-infrared (～ 1540 nm) electroluminescence (EL) from the LED with a structure of ITO/TiO<sub>2</sub>:Er/SiO<sub>2</sub>/n<sup>+</sup>-Si, in which TiO<sub>2</sub>:Er refers to the Er-doped TiO<sub>2</sub> film as the light-emitting layer. In this work, we co-dope ytterbium (Yb) into the TiO<sub>2</sub>:Er film in the aforementioned LED to significantly enhance the Er-related visible and near-infrared EL. It is revealed that a certain amount of Yb co-doping enables the TiO<sub>2</sub>:Er film to transform its crystal phase from anatase to rutile. Such a phase transformation reduces the symmetry of crystal field surrounding the Er<sup>3+</sup> ions incorporated into the TiO<sub>2</sub> host. Moreover, the substitution of over-sized Yb<sup>3+</sup> ions for Ti<sup>4+</sup> ions in the TiO<sub>2</sub> host leads to the distortion of the crystal field around the Er<sup>3+</sup> ions. The aforementioned symmetry-reduction and distortion of the crystal field increase the probabilities of the intra-4f transitions of Er<sup>3+</sup> ions. Due to the aforementioned reason, the Yb co-doping into the TiO<sub>2</sub>:Er film remarkably enhances the EL from the corresponding LED. It is believed that the strategy of Yb-codoping can be adopted to enhance the EL from the LEDs with other RE-doped TiO<sub>2</sub> films.

The Smaller the Better: Hosting Trivalent Rare-Earth Guests in Cu–P Clathrate Cages

Summary The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4 f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba 8−x R x Cu 16 P 30 , with the smallest pentagonal dodecahedral cages encapsulating La 3+ and Ce 3+ . Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

Effect of simultaneous K, and Yb substitution for Ca on the microstructural and thermoelectric characteristics of CaMnO3 ceramics

CaMnO3-based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca2+ by an equimolar mixture of K+ and Yb3+, Ca1-x(K0.5Yb0.5)xMnO3, with x = 0.05, 0.10, 0.15, and 0.20. XRD studies have confirmed that the thermoelectric phase is the major one in all samples. Microstructure has shown the formation of large crystals, and an increasing porosity when the substitution is raised. This evolution has been confirmed through density measurements. Electrical resistivity has been drastically decreased for the 0.10 substituted samples, compared with the 0.05 ones, slightly increasing for higher substitution. On the other hand, absolute Seebeck coefficient and thermal conductivity are lower when the substitution is raised. The best ZT values have been achieved for the 0.10 substituted samples, which are around the typical reported in the literature for higher doping level. These results clearly point out to a decrease of the necessary rare earth dopant content to achieve similar performances in CaMnO3 ceramics, which is of the main economic significance for their industrial production.

Effect of Yb Substitution on Microstructure and Superconducting Properties of Y1−xYbxBa2Cu3O7−δ Films

The purpose of this study was to improve the critical current density (Jc) of YBa2Cu3O7−δ (YBCO) superconducting films at high magnetic fields. Thin Y1−xYbxBa2Cu3O7−δ (Y1−xYbxBCO) superconducting films on LaAlO3 substrates were prepared by modified low-fluorine metal organic deposition method (LF-MOD) in order to investigate the effect of Yb substitution on the microstructure and superconducting properties of a YBCO-coated conductor. In this study, single-phased, c-axial-aligned Y1−xYbxBCO films were obtained. Yb doping had a little effect on the critical temperature (Tc) and transition width (ΔT) values of Y1−xYbxBCO films. An abnormal phenomenon was observed that the Jc of Y1−xYbxBCO films at low field was smaller than that of the pure YBCO film, but the Jc of Y1−xYbxBCO films at high field was much greater than that of the undoped YBCO film. Compared to pure YBCO film, the Jc values of Y0.75Yb0.25BCO and Y0.25Yb0.75BCO films were enhanced by a factor of 8 at 8 T, 65 K, which meant that chemical substitution of Yb into the Y site could improve flux pinning significantly under the high magnetic field in Y1−xYbxBCO coated conductors.

Optical study on intermediate-valence compounds Yb1−xLuxAl3**Project supported by the National Natural Science Foundation of China (Grant Nos. 11327806 and GZ1123) and the National Key Research and Development Program of China (Grant Nos. 2016YFA0300902 and 2017YFA0302904).

We report an optical spectroscopy study on intermediate valence system Yb1−xLuxAl3 with x = 0, 0.25, 0.5, 0.75, and 1. The Kondo temperature in the system is known to increase with increasing Lu concentration. Therefore, it is expected that the energy scale of the hybridization gap should increase with increasing Lu concentration based on the periodic Anderson model. On the contrary, we find that the spectral structure associated with the hybridization effect shifts monotonically to lower energy. Furthermore, the Lu substitution results in a substantial increase of the free carrier spectral weight and less pronounced plasma frequency reduction upon lowering temperature. We attribute the effect to the disruption of the Kondo lattice periodicity by the random substitution of Yb by Lu. The work highlights the importance of the lattice periodicity of the rare earth element for understanding the Kondo lattice phenomena.

Electric and dielectric properties of ytterbium substituted spinel ferrites

Ytterbium (Yb) substituted magnesium ferrite materials (MgYbxFe2−xO4 with x = 0.00, 0.025, 0.050, 0.075, 0.10) have been prepared by the Sol–gel method. XRD analysis revealed that the prepared samples are cubic spinel with single phase till the content ‘x’ equals 0.05. At higher content x ≥ 0.075, Yb substituted samples possessed YbFeO3 phase along with the cubic spinel phase. A significant decrease of ~34.7 nm in crystallite size is noted in response to the increase in Yb substitution level. The room temperature dc resistivity increases gradually from 3.47 × 107 to 2.63 × 108 Ω-cm as the substitution of Yb is increased. Temperature dependent DC electrical resistivity of all the samples exhibits semiconducting behavior. Yb substituted materials can be suitable to limit the eddy current losses for microwave applications. VSM indicated the existence of an appreciable fraction of ferrimagnetic properties at room temperature. The saturation magnetization of the samples decreases from 60 to 33 emu/g. Saturation magnetization and remanence decreased while coercivity increased with Yb substitution.

Kondo temperature and Heavy Fermion behavior in Yb1−xYxCuAl series of alloys

Results on x-ray diffraction, electrical resistivity, specific heat and magnetization on the Yb1−xYxCuAl series of compounds are reported. The analysis of the x-ray data shows the increase of the unit cell volume with the Y dilution. The electrical resistivity shows an evolution from Kondo lattice regime for x≤0.6 to single impurity behavior for x = 0.8 and 0.94. The electronic coefficient γ shows values of Heavy Fermion systems along the series for 0 ≤x<1. On the other hand, dc magnetic susceptibility measurements show typical curves of intermediate valence systems with a maximum around 25K. Below this maximum, the values of low temperature susceptibility (χ(0)) decrease with the increase of Y content. From the dependence of χ(0) and γ upon Y substitution, an increase of 12% of the Kondo temperature (TK) for x = 0.8 alloy respect to the reference YbCuAl (x = 0) is estimated. This is further supported by the evolution of the temperature of the maximum in the magnetic contribution of the specific heat. The overall results can be explained by the increase of the hybridization as consequence of negative pressure effects obtained by the chemical substitution of Yb by Y, thus leading to the increase of TK, in agreement with the Doniach's diagram.

The impact of Yb and Co on structural, magnetic, electrical and photocatalytic behavior of nanocrystalline multiferroic BiFeO3 particles

The nanocrystalline particles of BiFO3,co-doped with ytterbium and cobalt Bi1−xYbxCoyFe1−yO3 (BYCFO) were fabricated via micro-emulsion method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant. The dopant contents were kept x = 0.00, 0.025, 0.05, 0.075, 0.1, 0.125 and y = 0.00, 0.05, 0.1, 0.15, 0.2, 0.25 for six different compositions. The BYCFO-nanoparticles were investigated for structure, electric, dielectric, magnetic and photocatalytic properties. The X-ray diffraction (XRD) analysis confirmed the normal growth habitat Rhombohedral (R3c) phase on inclusion of ytterbium and cobalt ions as it is observed in undoped BiFeO3 multiferroic. However further doping of Yb+3 and Co+3 ions (x = 0.125, y = 0.25) resulted in some extra peaks, that is attributed to the formation of extra phase. The vibrating sample magnetometer recorded saturated magnetization (Ms) 0.385emu/g with remanent magnetization (Mr) 0.13emu/g for a coercivity of 405Oe which is higher than the undoped BiFeO3. The substitution of Yb+3 and Co+3 ions improved the canting angle and optimally aligned the sub lattices in ferromagnetic order. The grain size was found in the range of 20–24nm which is less than spiral spin modulation (≈ 62nm). The entire dielectric parameters showed smooth decreasing trend in low range frequency but at higher frequency (1.98GHz) resonance peaks appeared in the spectra. The insulating character was also enhanced up to 16.42 × 1010Ωcm−1, with increase in doping concentrations. The optical band gap was measured 1.5eV which was lower than the undoped BiFeO3 (2.15eV). The photocatalytic performance of co doped ceramic (Bi0.875Yb0.125Co0.25Fe0.75O3) was monitored using the textile dye Congo red. Approximately 28% of initial concentration (0.5ppm) was degraded by 200mg of ceramics in 42min under visible light irradiation. Being magnetic in nature, the Bi1−xYbxCoyFe1−yO3 particles could be separated by conventional magnetic bar.

Two-dimensional antiferromagnetic perturbation and enhanced ferroelectricity in h-Yb1−xHoxMnO3

The Low-temperature magnetic and electric properties of polycrystalline hexagonal rare-earth manganite h-Yb1−xHoxMnO3 (0 ≤ x ≤ 0.6, Δx = 0.2) were studied. The two-dimensional antiferromagnetic (AFM) perturbation along with the second AFM ordering have been observed, Néel temperature TN is found to be decreased by the Ho doping. The substitution of Yb by Ho atoms have a great influence on the electric properties, and the low-doping concentration is more favorable for the enhancement of electrical polarization which is sharply improved from 14.6µC/m2 in YbMnO3 (x = 0) to 131.4µC/m2 in Yb0.8Ho0.2MnO3 (x = 0.2).