Effect Of Co Substitution Research Articles

Structural, morphological, optical and dielectric investigations in cobalt doped bismuth ferrite nanoceramics prepared using the sol-gel citrate precursor method

In this work, the synthesis of un-doped and cobalt (Co)-doped nanoceramic samples of bismuth ferrite by cost-effective sol-gel citrate precursor technique are presented. Detailed investigations have been attempted to study the effect of Co substitution on the structural, morphological, dielectric and optical properties of bismuth ferrite prepared using the citrate precursor method. The main feature of these investigations is the relative elimination of secondary phase formation while preparing bismuth ferrite nanoceramic samples. X-ray diffraction analysis shows distorted rhombohedral perovskite structure for all compositions of BiFe1−xCoxO3 (x = 0.00, 0.03, 0.05, 0.10) nanoceramics, where the average crystallite size and induced strain in these samples are calculated using Scherrer’s method and Williamson–Hall equation, respectively. An increasing trend of average crystallite size with increase in dopant concentration was observed. Microstructural examinations of pure and doped BFO identified compact granular shaped microstructures with irregular size and shape but changed to uniform spherical shape after Co substitution up to 10 mol%. Confirmation of the uniform distribution of dopants throughout the sample has been carried out using elemental mapping studies. On the other hand, the chemical states of all the constituent elements were identified by X-ray photoelectron spectroscopic studies. Non-monotonic variations in the real part of dielectric values were observed with increasing Co concentrations. The optical absorption coefficient was found to increase by 35% in 10 mol% Co-doped BFO than that of pure BFO at 480 nm. Optical band gap studies depicted a striking inverse correlation of bandgap values and doping concentration up to 10 mol% Co substitution without varying the intrinsic structural feature of bismuth ferrite. Interestingly, the bandgap value of bismuth ferrite was varied from (2.08 ± 0.02) eV to (1.63 ± 0.02) eV, in the visible region. The results from present investigations suggest that synthesis techniques and chemical substitution need to be continuously optimized to get desired physical properties suitable for device applications such as photovoltaics.

Dependence of NiTi hydride stability by co-substitution by (Zr,Mg) onto Ti and (Cr,Cu) onto Ni: first-principles study

ABSTRACT The thermodynamics of hydride formation is one of the most important properties of the metal-hydrogen system, and states its potential for further uptake. For this reason, much research is focused on the use of first principle calculations as a predictive tool in the study of hydride stability. In this paper, First-principles density functional calculations were performed to predict the effect of co-substitution in NiTiH, Ti by Mg and Zr (x = 0.125, 0.25 and 0.375), as well as Ni by Cu and Cr (y = 0.125). Structural, thermodynamic stability and electronic properties were investigated. The formation enthalpy when Ti is substituted either by Mg or Zr with respect to their content is calculated and compared to the host NiTiH; it is found that the hydride stability decreases as Mg content increases while it increases when Zr content increases. The substitution of Ni by Cu destabilises the hydride while the stability of the hydride is enhanced when Ni is substituted by Cr. The simultaneous substitution of Ti by Mg (x = 0.375) and Ni by Cu (y = 0.125), leads to considerable destabilisation and an increase in cell volume of the hydride. The corresponding Ni0.875Cu0.125Ti0.625Mg0.375 compound is identified with optimum characteristics among the considered compositions, thereby can be considered as potential material for hydrogen storage.

Co-substitution tailored dielectric relaxation and electrical conduction in lanthanum orthoferrite

Effect of co-substitution on structural, dielectric and electrical conduction property of LaFeO3 is reported. Partial co-substitution of La by Na and Fe by Mn has been observed to cause substantial modification in structural property including lattice distortion in LaFeO3. Evidence of Jahn teller distortion has been noticed in Raman analysis due to presence of Mn3+ Jahn teller active ion at Fe lattice site. Raman analysis also indicated Fe–O–Fe bond weakening in LaFeO3 on co-substitution. Dielectric response provides evidence of temperature dependent polydispersive relaxations contributed by combined effect of dipolar and space charge relaxations. Temperature response of dielectric parameter (εr and tan δ) provided indication of phase transition that is similar to found in ferroelectric materials. The dielectric relaxations are studied in the framework of complex impedance and electrical modulus spectrum. The electrical response comprises both grain and grain boundary contribution in the reported polycrystalline sample and it seems consistent with brick layer model of electrical equivalent circuit. It is evident from the activation energy estimation from modulus and conductivity plot that the small polarons hoping are the key factor in both dielectric ordering as well as electrical conduction mechanism in co-substituted LaFeO3.

Effect of co-substitution of Zn2+/Zr4+ on Surface Morphology, Structure and Magnetic Properties of BaZnxZrxFe12-2xO19

The effect of co-doping of Zn2+/Zr4+ ions on surface morphology, structure and magnetic properties of BaZnxZrxFe12-2xO19 (x=0.00, 0.20,0.40,0.60,0.80, 1.00) synthesized using Pechini method has been investigated. XRD data reveals that the samples are phase pure and have no intermittent phase. The c/a parameter is <3.98 for all samples implying that they are M-type hexaferrites. The grain size increases with an increase in the composition of Zn2+/Zr4+ dopant seen using FE-SEM micrographs. The local crystal structure distortion with increasing Zn2+/Zr4+ dopant composition is confirm by Raman measurements. M vs H plots reveal that all the samples shows magnetic ordering. The highest Ms value has been noticed to be 68.43 emu/g in x=0.20 sample. The Hc value varies from 5350 Oe to 763 Oe with increase in dopant concentration. These materials have strong potential in magnetic recording applications.

Effect of Co substitution on thermal stability and magnetocaloric effects of Gd70Al20Fe10−xCox amorphous alloys

The alloys with great magnetocaloric effect (MCE) are expected to be a good alternative for magnetic refrigerantion. In this work, ribbons were prepared by the melt-spinning method using Gd70Al20Fe10−xCox (x = 0, 2, 4, 6, 8 and 10) alloys. Crystal structure, thermal stable, specific heat and magnetic properties of the ribbons were investigated by x-ray diffraction, Dynamic flow differential scanning calorimetry and Physical Properties Measurement System. Results show all samples are in amorphous state, and their onset crystallization temperatures (595–634 K) are higher than the magnetic transition temperature, which contributes to the stable of amorphous structures in practical application. In applied magnetic field of 5 T, the value of magnetic entropy change ∣ΔSM∣ increases from 7.1 to 8.7 J · kg−1 · K−1 near the Curie temperature (151–114 K) of Gd70Al20Fe10-xCox alloys (x = 0, 2, 4, 6, 8 and 10) , respectively, which is ascribed to the exchange interaction between magnetic atoms Co and Fe; the full width at half maximum (FWHM) of ΔSM and refrigeration capacity (RC) increase by 91% and 56% compared with those of pure Gd, respectively; the adiabatic temperature change are in the range of 3.4–3.7 K for the alloys. In addition, all alloys undergo a second order ferro-paramagnetic phase transition, which is certified by the Arrott plots and universal curves.

Effect of Co substitution and magnetic field on the morphologies and magnetic properties of CeO2 nanoparticles

Abstract Pure and Co-doped CeO2 nanoparticles were synthesized successfully by the solvothermal method. The effect of Co substitution and external magnetic field on the morphologies and magnetic properties of nanoparticles was investigated. Results showed that synthesized Co-doped CeO2 had the face-centered cubic structure and no other impurities existed in the samples with the increase of Co concentration from 5 to 75 wt%. The increasing Co concentration made the morphologies of Co-doped CeO2 nanoparticles vary from the hollow sphere, solid sphere to rod-like shape. The applied external magnetic field of 5T decreased the nanoparticle size effectively including the diameter of hollow sphere with low Co concentration and rod-like particles with high Co concentration. Moreover, the wall thickness of hollow sphere particles was also decreased from 35 nm to 18 nm for pure CeO2. The Co-doped CeO2 nanoparticles showed the weak ferromagnetic behavior. With the increase of Co concentration, the saturation magnetization (Ms) value increased first and then decreased. The Co-doped CeO2 with 30 wt% showed the highest value of 3.65 × 10−2 emu/g (Ms). The Ms value of Co-doped CeO2 prepared in 5T showed an increasing trend with the Co concentration. The highest value (Ms) reached 4.21 × 10−2 emu/g for doped CeO2 with 75 wt% Co.

Effect of bimetallic (Ca, Mg) substitution on magneto-optical properties of NiFe2O4 nanoparticles

Nanoparticles (NPs) of calcium and magnesium co-substituted nickel ferrite with the chemical composition CaxMgxNi1–2×Fe2O4 (0.00 ≤ x ≤ 0.05) NPs were prepared hydrothermally. The (Ca, Mg) co-substitution effect on morphological, structural, optical and magnetic properties of NiFe2O4 NPs was analyzed via FT-IR, XRD, TEM, SEM, DRS and VSM techniques. The magnetization of CaxMgxNi1–2×Fe2O4 (0.00 ≤ x ≤ 0.05) NPs were examined and analyzed at room temperature (300 K; RT) and low temperature (10 K). The specific magnetic parameters such as saturation magnetization Ms, remanence Mr, coercivity Hc, squareness ratio (SQR=Mr/Ms) and magnetic moment nB of Ni1–2×MgxCaxFe2O4 (0.00 ≤ x ≤ 0.05) NPs were determined and evaluated. The M(H) curves exhibit superparamagnetic behavior at RT and ferrimagnetic nature at 10 K. The substitution significantly changes the magnetizations and coercivity data. An increase in the Ms, Mr, Hc and nB values was observed in substituted products compared to pristine one. The highest values were obtained for x = 0.05 product. The SQR values are found to be below than 0.5, which can be attributed to surface spin disorder effects. The obtained magnetic results are primarily derived from the substitution with Mg and Ca that will strengthen the super exchange interactions.

Remarkable effect of Co substitution in magnetite on the reduction removal of Cr(VI) coupled with aqueous Fe(II): Improvement mechanism and Cr fate

The interaction between magnetite and aqueous Fe(II) profoundly impacts the mineral recrystallization, trace-metal sequestration, and contaminant reduction. The iron ions in natural magnetite are extensively substituted by other cations. It is still unclear whether the substitution with thermodynamically favorable redox repairs (e.g., Co2+/Co3+) plays a vital role in the reducing capability of the coupled system. Herein, a series of Co-substituted magnetite samples (Fe3−xCoxO4, 0.00 ≤ x ≤ 1.00) were synthesized and tested for the reductive removal of Cr(VI) in the presence of Fe(II). Fe3−xCoxO4 had a spinel structure with the preferential occupancy of Co2+ on octahedral sites. No visible variation in the BET surface area was observed, whereas the surface site density increased gradually with Co substitution. Cr(VI) was found first adsorbed on the Fe3−xCoxO4 surface and then reduced to Cr(III) by the structural Fe2+ and the absorbed Fe(II), accompanied by the oxidation of bulk Fe2+ and surface Fe(II) in Fe3−xCoxO4 without phase transformation. The Cr(III) was precipitated on the Fe3−xCoxO4 surface with Fe(III), or substituted octahedral Fe in Fe3−xCoxO4. Both the reaction kinetics and the electron transfer efficiency revealed that Co substitution significantly improved the reactivity of Fe3−xCoxO4/Fe(II) towards Cr(VI) reduction. This was ascribed to the presence of the redox pairs Co2+/Co3+ and Fe2+/Fe3+ accelerating electron transfer from the Fe3−xCoxO4 interface to Cr(VI).

Effect of co-substitution of Co2+ and V5+ for Fe3+ on the magnetic properties of CoFe2O4

Different chemical compositions in Co1+2xVxFe2-3xO4 (0 ≤ x ≤ 0.1) have been synthesized by the conventional solid-state reaction method and processed under identical conditions. The materials are investigated to assess the impact of change in the oxidation states of metal ions on structural and magnetic properties of cobalt ferrite. Rietveld refinement of the X-ray diffraction patterns revealed a single phase nature of all compositions with cubic spinel structure. The cubic lattice parameter was found to decrease non-linearly from 8.393 Å for x = 0 to 8.377 Å for x = 0.1, due to the effect of ionic size and valency of the substituted metal ions. Sintered co-substituted compositions exhibited smaller grains against unsubstituted counterpart, due to low melting point of raw material V2O5. Strong experimental evidence of V substitution for Fe at the tetrahedral sites of the spinel ferrite has been extracted from the Raman spectral analysis. Saturation magnetization (Ms) was observed to decrease from 452 kA/m for x = 0–411 kA/m for x = 0.1. Coercivity (Hc) and magnetocrystalline anisotropy (K1) were also found to follow the same trend. Variation of the structural and magnetic parameters is attributed to the changes in the oxidation state of Co from 2 + to 3 + as it is confirmed from the results of XPS analysis.

Enhancement of Magnetoresistance by Co Substitution in Pr0.6Sr0.4Mn1−&lt;italic&gt;x&lt;/italic&gt;Co&lt;italic&gt;x&lt;/italic&gt;O3

We investigate the effect of Co substitution on magnetism, electrical resistivity, and magnetoresistance (MR) in Pr0.6Sr0.4Mn1− x Co x O3( $x=0-0.2$ ). The parent compound Pr0.6Sr0.4MnO3 is a double exchange (DE) ferromagnet with a ferromagnetic (FM) transition at $T_{C} = 305$ K. The long-range FM order persists for $x=0.05$ with a radical downshift in $T_{C}$ (260 K). A decrease in magnetization as well as a drastic increase in electrical resistivity ( $\rho \sim ~0.02~\Omega \cdot \text {cm}$ for $x=0$ to $\sim 10^{7}~\Omega \cdot \text {cm}$ for $x=0.2$ at 10 K) with Co doping indicates the weakening of DE interaction and the evolution of glassy magnetic ground state. For both $x=0$ and 0.05, $\rho $ shows a prominent peak at their respective $T_{C}$ , whereas such a feature is absent for $x\ge 0.1$ . A large enhancement in MR at low temperatures occurs with increasing Co doping (from −45% for $x=0$ to −85% for $x=0.2$ at 10 K at 7 T magnetic field). The occurrence of such a huge MR at low temperatures for Co-doped compounds could be either due to spin-dependent tunneling between FM clusters with the spin-glass-like interface within grains or suppression of spin fluctuations.

Effect of Co-substitution on the Vibrational, Magnetic, and Dielectric Properties of Copper Ferrites Obtained by Microwave-Assisted Hydrothermal Method

Co-substituted copper ferrites have been synthesized by a microwave-assisted hydrothermal method. X-ray diffraction confirms that Cu1.0Fe2.0O4 presents both tetragonal and CuO monoclinic phases, whereas the Co-substituted copper ferrites are cubic single-phase structures. All materials were crystallized as ultrafine particles with very low sublattice distortions, and the lattice constants vary with the degree of substitution. Fourier-transform infrared and Raman spectroscopies suggest a short range of the crystal lattices. Magnetic analyses demonstrated that each of the ferrites exhibits soft magnetic behavior with low hysteresis loss and coercive force. Electrochemical impedance data indicate a strong relative permittivity and weak dielectric loss tangent to the Co-substituted samples.

Effects of Co-Substitution of Layered Perovskite Lsfo on Oer Activity in Alkaline Media

Introduction Oxygen evolution reaction (OER) is the fundamental processes for water splitting and rechargeable metal-air batteries in alkaline media. Ir-based catalysts are regarded as one of the promising active OER catalysts, however the use of such noble metal-based materials leads to high cost. Perovskite metal oxide has been attracted much attention as the alternative low cost materials. Among them, the layered perovskite, LaSr3Fe3O10 (LSFO) shows enhanced ORR activity thus is expected as a bifunctional catalyst for ORR and OER1). Moreover, ABxB’1−xO3 structure shows improved OER activity compared to the simple perovskites 2). In this study, we prepared the layered perovskite LaSr3Fe3-x Co x O10-δ (x = 0, 0.15, 0.3, 0.6, 1.5, 3.0). Their OER activity and performance as a cathode catalyst for Zn-air batteries were studied. Experimental Synthesis of LaSr3Fe3-x Co x O10-δ was carried out by a nitrate-citrate method. Stoichiometric metal nitrates and citric acid were dissolved in water (metal : citric acid = 1 : 1 mol) and the solution was concentrated at 120 oC for several hours, followed by drying at 450°C for 1 hour. After drying, the obtained powders were pelletized into a disk, then calcined in air at 1400 oC for 20 hours. LaSr3Fe3-x Co x O10-δ electrode was fabricated by pressing the calcined pellet at 15 MPa for 10 minutes and sintering at 900 oC for 10 hours. H type-cell consisted of the prepared LaSr3Fe3-x Co x O10-δ as a cathode, platinum plate as an anode, 4.0 mol dm-3 KOH as an electrolyte, and Celgard #3401 as the separator was used for OER measurement under air atomosphere. For zinc-air battery tests under O2 atmosphere, zinc foil and ZnO saturated 4.0 mol dm-3 KOH were instead used as anode electrode and electrolyte, respectively. Results and Discussion For choronoamperometry tests, the LaSr3Fe3-x Co x O10-δ electrode showed higher OER activity than the Pt/C and Ir/C electrodes. As shown in Figure 1(a), the OER activity of LaSr3Fe3-x Co x O10-δ electrodes is sensitive to the amount of Co substitution. This result suggests that Co substitution into Fe-occupied site is effective in improvement of the OER activity of LSFO. The LaSr3Fe3-x Co x O10-δ electrode also shows superior charge/discharge energy efficiency than the Pt/C electrode in zinc-air battery cycling. Moreover, it is found that Co substitution to LSFO unfortunately led to decrease in ORR activity while somewhat effective on OER activity improvement under O2 atmosphere. The catalytic behavior of LaSr3Fe3-x Co x O10-δ is highly complicated, however the valence of B-site elements probably has a significant effect on determining OER and ORR activity. References 1) T. Takeguchi, et al., J. Am. Chem. Soc., 135, 11125 (2013). 2) A. Vignesh, et al., ACS Appl. Mater. Interfaces, 8, 6019 (2016). Acknowledgement This work is partly supported by NEDO. Fig.1. (a) Current density of LaSr3Fe3-x Co x O10-δ electrodes as a function of the amount of Co substitution (x). Current densities were recorded at 10 hours after applying potential at 1.55 V vs. RHE. (b) Charge/discharge curves of Pt/C and LaSr3Fe3-x Co x O10-δ (x = 1.5) electrodes in zinc-air battery. Current density of 0.1 mA cm-2 for 12 hours each. Figure 1

Evolution of structure and superconductivity in Ba(Ni1−xCox)2As2

The effects of Co-substitution on Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ ($0\leq x\leq 0.251$) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi$_2$As$_2$ exhibits a first order tetragonal to triclinic structural phase transition at $T_s=137 K$ upon cooling, and enters a superconducting phase below $T_c=0.7 K$. The structural phase transition is sensitive to cobalt content and is suppressed completely by $x\geq0.133$. The superconducting critical temperature, $T_c$, increases continuously with $x$, reaching a maximum of $T_c=2.3 K$ at the structural critical point $x=0.083$ and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi$_2$As$_2$ substitutional studies, which show an abrupt change in $T_c$ at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ exhibits a dome-like phase diagram centered around the first-order critical point. Together with an anomalously large heat capacity jump $\Delta C_e/\gamma T\sim 2.2$ at optimal doping, the smooth evolution of $T_c$ in the Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ system suggests a mechanism for pairing enhancement other than phonon softening.

Magneto-optical and microstructural properties of spinel cubic copper ferrites with Li-Al co-substitution

Nanospinel Li2xCu1-xAlyFe2-yO4 ferrites with composition x = y = 0.0, 0.2, 0.3 and 0.4, were successfully synthesized via hydrothermal method. The effect of co-substitution (Li and Al) on structural, morphological and magnetic properties of CuFe2O4 nanoparticles were investigated using Powder X-ray Diffraction (XRD), Fourier-Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and Mossbauer spectroscopic techniques. The cation distribution of all composition was calculated. Both XRD and FT-IR analyses confirmed the synthesis of single-phase spinel cubic product for all the substitutions. Mossbauer investigation showed that the Li1+ and Al3+ ions occupied B-sites. Nonetheless, some amounts of Li1+ occupy A-site. The magnetization hysteresis loops M (H), revealed that the final products with x, y = 0.0, 0.3 and 0.4 exhibit superparamagnetic (SPM) behavior at room temperature, however the composition x, y = 0.2 displays a ferromagnetic-like (FM) behavior. The saturation magnetization (Ms) reduces with rising the Li and Al contents. Compared to pristine CuFe2O4 spinel, the remanent magnetization (Mr), coercive field (Hc) and the magneto-crystalline anisotropy fields (Ha) improved for products synthesized with x, y = 0.2 and then decrease for x, y = 0.3 and 0.4. The squareness ratio Mr/Ms are less than 0.500, which suggest the single domain nanoparticles with uniaxial anisotropy for Li2xCu1–xAlyFe2-yO4 (0.0 ≤ x, y ≤ 0.4) nanoparticles. The magneto-crystalline anisotropy constant (Keff) value is improved for Li0.8Cu0.6Al0.2Fe1.8O4 (i.e. x, y = 0.2) magnetic nanoparticles and then decreased for higher Li and Al contents, due to the replacement of Cu and Fe ions with respectively Li and Al ions.

Effects of Co-substitution on the reactivity of double perovskite oxides LaSrFe2-xCoxO6 for the chemical-looping steam methane reforming

The double perovskite oxides (DPOs) LaSrFe2-xCoxO6 (x = 0, 0.2, 0.4, 0.6, 0.8) were investigated as oxygen carriers for the chemical looping steam methane reforming (CL-SMR). The fresh oxides were prepared by micro-emulsion method and their physical and chemical properties were characterized by X-ray diffraction, H2-temperature programmed reduction and X-ray photoelectron spectroscopy technologies. Meanwhile, isothermal reactions for methane reforming and steam splitting were carried out in a fixed-bed reactor to determine the influences of Co-substitution on the reactivity of LaSrFe2-xCoxO6. The substitution of metal Co has no obvious effect on the crystal structure of double perovskite, but induces a certain degree of Fe/Co disorder generating oxygen vacancies and/or higher oxidation states of metal cations. Synergistic interaction between surface metal ions, such as (Fe4+/Fe5+-O2--Co2+) and (Fe3+-O2--Co3+), plays a positive effect for the dissociation of methane. The activity may be more likely to be associated with the active oxygen species in connection with Co species on the DPOs surface and abundant of syngas was generated due to the concordant of methane dissociation with the lattice oxygen diffusion. Comprehensively considered, an optimal range of the degree of Co substitution is x = 0.4–0.6 for LaSrFe2-xCoxO6, probably converting 70% of CH4 into CO and H2 with molar ratio around 2:1. At the reduced states, the ability of DPOs for steam splitting is primarily associated with the oxygen vacancies after oxygen consumption. The substitution of metal Co slightly enhances the hydrogen production capacity and resistance to carbon formation, achieving the average hydrogen yields at 2.89–3.33 mmol/g oxygen carrier and 1.46–1.61 wt% of carbon depositions.

Near total magnetic moment compensation with high Curie temperature in Mn2V0.5Co0.5Z (Z = Ga,Al) Heusler alloys

Mn2V1−xCoxZ (Z = Ga,Al and x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys have been synthesized to investigate the effect of Co substitution at the V site on the magnetic moment and Curie temperature of half-metallic ferrimagnets Mn2VGa and Mn2VAl. Near total magnetic moment compensation was achieved with high Curie temperature for x = 0.5 composition. The Co substituted alloys show a non linear decrease in lattice parameter without altering the crystal structure of the parent alloys. The end members Mn2VGa and Mn2CoGa have the saturation magnetization of 1.80 µB/f.u. and 2.05 µB/f.u. respectively whereas for the Mn2V0.5Co0.5Ga alloy, a near total magnetic moment compensation (0.10 µB/f.u.) was observed due to the ferrimagnetic coupling of Mn with parallelly aligned V and Co. The Co substituted Mn2VAl has also shown a similar trend with compensated magnetic moment value of 0.06 µB/f.u. for x = 0.5. The Curie temperatures of the alloys including the x = 0.5 composition are well above the room temperature (more than 650 K) which is in sharp contrast to the earlier reported values of 171 K for the (MnCo)VGa and 105 K for the (MnCo)VAl (substitution at the Mn site). The observed TC values are highest among the Mn2V based fully compensated ferrimagnets. The magnetic moment compensation without significant reduction in TC indicates that the V site substitution of Co does not weaken the magnetic interaction in Mn2VZ (Z = Ga,Al) alloys which is contrary to the earlier experimental reports on Mn site substitution.

Effect of Co-substitution on the sintering characteristics and microwave dielectric properties of Li2MgTiO4 ceramics

Rock-salt-structured Li2(Mg1−xCox)TiO4 (x = 0, 0.05, 0.10, 0.15 and 0.2) ceramics were successfully prepared via the conventional solid-state ceramic route in the present work. The effects of Co2+ content on sintering characteristics, crystal structure and microwave dielectric properties of Li2MgTiO4 ceramics were systematically investigated. Raman spectra and X-ray diffraction analysis revealed that the Li2(Mg1−xCox)TiO4 ceramics could form single phase within the range of 0.00 ≤ x ≤ 0.20. As the Co2+ content gradually increased, the dielectric constant of the solid solution gradually increased from 15.60 to 16.93, which was closely related with the variation of polarizability as well as the Raman shift in typical vibration modes. The thermal stability was also adjusted to a certain extent, and near-zero τf values could be found at x = 0.05 and 0.10. Although the dielectric loss gradually increased with the increasing Co2+ content, a good combination of microwave dielectric property of εr = 15.7, Q × f = 119,600GHz and τf = −2.67ppm/°C could be found in the Li2(Mg0.9Co0.1)TiO4 ceramics sintered at 1400°C.

Effect of co-substitution of Sm3+ and Fe3+ ions on structural and dielectric properties of BaTiO3 ceramics

The material series of polycrystalline ferroelectric ceramics with compositional formula (Ba1-xSmx)(Ti1-xFex)O3 (with 0 ≥ x ≥ 0.01 in steps of 0.0025) was prepared by solid-state reaction method. The samples were sintered at 1300 °C (for x = 0) and 1325 °C for (x > 0). The sintered samples were subjected to X-ray diffraction (XRD) analysis and found to have single phase with tetragonal perovskite structure. Average grain size decreases with increase in substituent content. Dielectric behavior was studied as a function of temperature at different frequencies (1, 10,100,1000 kHz). The lattice constant ‘c’, tetragonality‘c/a ratio’ and Curie temperature ‘Tc’ was found to decrease with increase in the substituent content whereas the room temperature dielectric constant increases with substituent content. Large value of temperature coefficient of capacitance ‘Tcc’> 10%/°C near Tc was observed for all the samples.

The effect of Co substitution on the magnetic and magnetocaloric properties of Gd3Ru

The effects of Co substitution on the structure, magnetic properties, and magnetocaloric effect of Gd3Ru1−xCox (0.05 ≤ x ≤ 0.20) alloys have been investigated by X-ray diffraction and magnetization measurements. The Curie temperatures varied between 60 K and 92 K with Co substitution for Ru. With an applied magnetic field change (ΔH) of 50 kOe, the maximum values of magnetic entropy change (−ΔSM) were determined to be 25.8, 23.1, 19.4, and 10.8 J/kg K for compositions with x = 0.05, 0.10, 0.15, and 0.20, respectively. The corresponding refrigeration capacities (RCs) for the alloys were reasonably large and calculated to be 495, 475, 467, and 517 J/kg. The magnetic phase transitions in the Gd3Ru1−xCox (0.05 ≤ x ≤ 0.15) alloys are of first-order. In the Gd3Ru0.80Co0.20, the first-order magnetic phase transition disappears and the transition is broadened hence it increases in RC. The high −ΔSM values and accompanying large RCs for the Gd3Ru1−xCox (0.05 ≤ x ≤ 0.20) alloys qualify them as potential candidates for magnetic refrigeration applications near liquid nitrogen temperature.

Photoluminescence Properties of Double Perovskite Tantalates Activated with Mn4+, AE2LaTaO6:Mn4+ (AE = Ca, Sr, and Ba)

Tetravalent manganese is known as one of the candidate luminous centers to obtain red emission. There are still unclear factors in Mn4+-activated oxide phosphors to achieve intense emission. In this paper, we studied the photoluminescence properties of double perovskite-type tantalates AE2LaTaO6 (AE = Ca, Sr, and Ba) activated with Mn4+. All AE2LaTaO6:Mn exhibited Mn4+-emission in the deep red region under excitation by near-ultraviolet-green light (300–570 nm) at room temperature. Co-substitution of Mg2+, Al3+, and Ti4+ compensates unbalanced charge caused by oxygen defects, resulting in the enhancement of Mn4+-emission. The present cosubstitution effect is different from the usual cosubstitution, such as the replacement of two Al3+ by Mn4+ and Mg2+, taking into consideration the charge balance between cations. Theoretical calculation of band structures based on density functional theory suggests the presence of two kinds of quenching schemes in AE2LaTaO6:Mn, photoionization and electron transfer from va...