Thermoelectric properties of Ca3Co4−xMnxO9+δ with x = 0.00, 0.05, 0.10, and 0.15

Ca₃Co_4?xMn_xO_9+δ (x?=?0.00, 0.05, 0.10, and 0.15) sample were prepared by conventional solid state synthesis. The thermoelectric properties were measured at 15 K–300 K. The XRD results revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers were holes over the entire temperature range. Both the electric resistivity and the thermopower increased with increasing Mn content. Ca₃Co_3.95Mn_0.05O_9+δ had the highest power factor of 3.40 μW cm^?1 K^?2 at 163 K, representing an improvement of about 187 % compared to undoped Ca₃Co₄O_9+δ. These results suggested that there is scope for improving the thermoelectric characteristics via partial substitution of Mn for Co.     

Microwave and electrical behavior of Co2+ and Ru4+ ions substituted Ba-Sr sintered ferrite

The complex permittivity and complex permeability of synthesized M-type hexagonal ferrite powders, Ba_0.5Sr_0.5Co_xRu_xFe_(12-2x)O₁₉ (x?=?0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) are measured at X-Band. The experimental results conclude that Co²⁺ and Ru⁴⁺ ions substitution enhances electromagnetic properties, rendering the use of ferrite for lossy applications. The acceleration in hoping mechanism between Fe²⁺ and Fe³⁺ ions leads to dominance of ??? and ??? over ??? and ??? along entire frequency band.     

The effect of Bi substitution on phase formation and low temperature sintering of Y-type hexagonal ferrite

Polycrystalline Y-type hexagonal ferrite, with composition of Ba_2?x Bi _x Zn_0.8Co_0.8+x Cu_0.4Fe_12?x O₂₂ (x?=?0～0.4), was prepared by the solid state reaction method. The effect of Bi substitution on phase formation, sintering process and magnetic properties were investigated in detail. The phase formation process was characterized by the means of powder X-ray diffraction (XRD). Bi³⁺ can substitute Ba²⁺ in Y-type hexagonal ferrite as divalent metal ion Co²⁺ substitute Fe³⁺ at the same time for electrovalence balance. As Bi amount is less than 0.3, the phase formation of Y-type hexagonal ferrite will not be destroyed. As Bi amount further increases, the lattice mismatch induced by the difference in ionic radii of Bi³⁺ and Ba²⁺ ions prevents the formation of pure Y-type phase. The samples with proper Bi substitution (0.05?<?x?<?0.3) have much lower phase formation temperature than that of the samples without Bi substitution. Bi substitution can also promote the sintering process. As x?>?0.1, the samples can be sintered well under 900 °C without any other addition. These materials are suitable for multilayer chip inductive components and devices.     

Normal-to-relaxor ferroelectric phase transition and electrical properties in Nb-modified 0.72BiFeO<Subscript>3</Subscript>-0.28BaTiO<Subscript>3</Subscript> ceramics

Preparation and electrical properties of sintered bodies consisting of monophase cubic spinel oxides, Cr_XMn_1.5Co_(1.0-X)Ni_0.5O₄ (0 ≦ X ≦ 0.42), were investigated. Specimens with compositions within X = 0.42 were prepared as starting materials. The element of Cr was used to exchange Co³⁺ in octahedral sites (B sites) with Cr³⁺ so that the hopping mechanism can be discussed. The sintered bodies with mono cubic spinel structure were confirmed to be prepared by heat-treatment for 48 h in air at 1000 °C to convert them into a cubic spinel structure after sintering at 1400 °C. The semiconductive characteristics of the sintered bodies were determined as p-type because the Seebeck coefficients were all positive. The electrical conduction of the sintered bodies was concluded to be controlled by the small polaron hopping mechanism. In the region 0.1 ≦ X ≦ 0.42, the lattice constant increases and electrical conduction (σ) decreases linearly with increasing Cr concentration. The decrease in σ and the increase in the lattice constant corresponded to the increase in Cr concentration by which the jumping distance of electrons between Mn³⁺ and Mn⁴⁺ is lengthened.     

Development of a New MnZn-Ferrite Soft Magnetic Material for High Temperature Power Applications

At power electronic applications (e.g. in automotive, lighting, electrical equipment etc.) the inductive components that consist the heart of the power transformers are made of ceramic ferromagnetic materials of the type (Mn_xZn_yFe^{2 +}_{1 – x – y})Fe^{3 +}₂O₄. Usually they are designed in such a way in order to exhibit optimum magnetic performance and electromagnetic power loss minimum at 80–100C, which is the steady state operation temperature region for most devices. However, the continuous miniaturization of electric and electronic equipment associated with a continuous increase in the density of electronic components has as unavoidable consequence the gradual shift of the steady state operation temperature to higher levels. The need is therefore becoming obvious for the development of new power soft magnetic materials optimized to operate at higher temperatures than those at which current existing materials operate. In the present work the development is described of such a new soft ferrite material having the chemical composition (Mn_0.76Zn_0.17Fe^{2 +}_0.07)Fe^{3 +}₂O₄, initial magnetic permeability of 1800 (measured at a frequency f = 10 kHz, an induction level B < 0.1 mT and a temperature T = 25C), Curie temperature of 225C and electromagnetic power losses < 350 mW/cm³ measured at a temperature of 140C, frequency of 100 kHz and a magnetic field strength of 200 mT. The material has been successfully introduced to production and is now commercially available. The largest application is offered by the automotive industry in particular for tackling high temperature operating problems arising when control is being done near the engine (near the engine electronics).     

The influence of lithium content in xLi[Li1/3Mn2/3]O2 · (1-x)Li[NiaCobMn(1-a+b)]O2 cathode materials prepared by co-precipitation method

The Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode system with various compositions of excess lithium in the range of x?=?1.3?~?1.9 was added to Li_x(Ni_aCo_bMn_(1-a+b))O₂ cathode materials synthesized using the co-precipitation method to investigate its microstructure and electrochemical properties. The X-ray diffraction (XRD) patterns of the prepared powders showed a hexagonal α–NaFeO₂ structure (space group: R-3 m, 166) and the existence of Li₂MnO₃ phase in the composite structure. The morphology of the prepared powders consisted of spherical agglomerates with particle size varying from 5 to 8 μm. The size increased with increasing Li content. The observed discharge capacity for the Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode (x?=?1.3, 1.5, 1.7, 1.9) for the first cycle was 46, 126, 206, and 94 mAhg^-1 for Li_1.7(Ni_aCo_bMn_(1-a+b))O₂, respectively_.     

A comparative study of high temperature properties of cobalt-free perovskites

Co-free perovskites with chemical composition Ba_0.5Sr_0.5Fe_0.8M_0.2O_3-δ (M = Ni, Cu, Zn) were synthesized by the modified Pechini method, and their structure and microstructure were characterized by XRD and SEM. Oxygen content, electrical resistivity and Thermal Expansion Coefficient (TEC) were evaluated in air between room temperature and 900 °C. The high-temperature properties of these perovskites were compared with those of Co containing Ba_0.5Sr_0.5Fe_0.8Co_0.2O_3-δ perovskite. The highest electrical conductivity was obtained for Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ, with values of 47.6 Scm^?1 at 544 °C. This same composition also exhibits the highest oxygen vacancies concentration: 3-δ = 2.61 at room temperature. In contrast, the Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3-δ, showed lower electrical conductivity suggesting that the Zn⁺² ions block electron transport. Co-free perovskites seem to be stable at high temperatures for long term periods. However, these compounds suffered degradation at room temperature in samples stored in air.     

Structure and properties of Zn-doped CoFe2O4 thin films via a sol–gel method

Zn-doped cobalt ferrite Co_0.9Zn_0.1Fe₂O₄ (CZFO) films with the spinel structure were fabricated on Pt(111)/Ti/SiO₂/Si(100) using a sol-gel method, and the effect of annealing temperature and time on structure and magnetic properties of the CZFO thin films were investigated. The coercivity and saturation magnetization of the films are not sensitive to annealing time, and increase with a rise in the annealing temperature below 800 °C. The CZFO thin films annealed at 800 °C show the best crystallization and the highest coercivity (3.5 kOe), and above 800 °C, the coercivities of the films decrease as a result of formation of multi-domains, while the saturation magnetization comes to stable.     

Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn_0.9Cu _x Mn_2.1-x O₄ (0.1?≤?x?≤?0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn_0.9Cu _x Mn_2.1-x O_\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn³⁺ ions at the B sites. Cu2p_3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn_0.9Cu _x Mn_2.1-x O₄ varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.     

Structural and electrochemical properties of LiNi0.7Co0.15Mn0.15O2 thin film prepared by high frequency hybrid direct current and radio frequency magnetron sputtering

A LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode has been successfully prepared by hybrid direct current - radio frequency magnetron sputtering onto glass substrate from the LiNi_0.7Co_0.15Mn_0.15O₂ target and post-annealed by the rapid thermal annealing process. Its structure and morphology were characterized by X-ray diffraction, and scanning electron microscopy while its chemical compositions were confirmed with the inductively coupled plasma atomic absorption spectrophotometer, Raman spectroscopy, Auger electron spectroscopy, and glow discharge spectrometer. Its electrochemical properties were measured by galvanostatic charge - discharge test and cyclic voltammetry. First discharge capacity of 73 μAh?cm^?2?μm^?1 was obtained from a half cell with the LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode and lithium metal anode in the potential range of 4.3?~?2.5 V at 30 μA and its coulombic efficiency was more than 99 %.     

Thermoelectric properties of Ca3-xEuxCo3.95Ga0.05O9+δ (0 ≤ x ≤ 0.10)

Polycrystalline samples of Ca_3–xEu_xCo_3.95Ga_0.05O_9+δ (x?=?0.00, 0.02 and 0.10) have been prepared by conventional solid-state synthesis and their thermoelectric properties measured at 25 K to 300 K. The XRD results revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were simultaneously increased with increasing Eu³⁺ content. The total thermal conductivity decreased with increasing Eu³⁺ content. A maximum dimensionless figure of merit of 0.033 at 300 K was reached for Ca_2.9Eu_0.1Co_3.95Ga_0.05O_9+δ, which is about 27 % higher than that of the undoped sample. These results suggest that the Eu is an effective doping element for improving the thermoelectric properties of Ca₃Co_3.95Ga_0.05O_9+δ.     

Effects of partial substitution of Fe for Co on the low-temperature thermoelectric and magnetic properties of Ca2.7Bi0.3Co4-xFexO9+δ (0 ≤ x ≤ 0.15)

Polycrystalline samples of Ca_2.7Bi_0.3Co_4-xFe_xO_9+δ (x?=?0.00, 0.025, 0.05, 0.10 and 0.15) have been prepared by conventional solid-state synthesis and their thermoelectric and magnetic properties measured. The X-ray diffraction patterns revealed that all the samples are single phase. The electrical resistivity results indicated that all the samples obey the variable range hopping in the low temperature regime. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were increased with increasing Fe content. Among the samples, Ca_2.95Bi_0.10Co_3.95Fe_0.05O_9+δ had the highest dimensionless figure of merit of 0.102 at 300 K. Magnetic measurements indicated that all the samples exhibit a low-spin state of cobalt ion. The effective magnetic moments were decreased with increasing Fe content.     

Synthesis and characterization of rare-earth elements substituted Ni-Zn ferrites

ABSTRACT

The spinel Ni_0.7Zn_0.3RE_0.04Fe_1.96O₄ ferrites with RE?Ce and Y are fabricated by the polyacrylamide gel method. The effect of rare earth ions substitution for iron ions on the structure, morphology, electromagnetic and microwave-absorbing properties of Ni-Zn ferrites are investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), thermogravimetric and differential thermal analysis (TG-DTA) and HP8510B network analyzer, respectively. The results indicate that Ni_0.7Zn_0.3RE_0.04Fe_1.96O₄ ferrites form a pure cubic spinel structure, and Ce³⁺ and Y³⁺ substitute into the crystal lattice. Both the real ?′ and imaginary ?″ parts values of complex permittivity for Ni_0.7Zn_0.3RE_0.04Fe_1.96O₄ ferrites are higher than those for Ni-Zn ferrites in X-band (8.2-12.4 GHz) frequency range. When RE ions substitute for iron ions, the real μ′ and imaginary μ″ parts values of complex permeability for Ni_0.7Zn_0.3RE_0.04Fe_1.96O₄ ferrites decrease and increase, respectively. The microwave-absorbing properties are better for RE-substituted Ni-Zn ferrites than Ni-Zn ferrites. For Ni_0.7Zn_0.3Ce_0.04Fe_1.96O₄ ferrites, the minimum loss is ?12.5 dB at 18 GHz for an absorber thickness of 2 mm.     

Effect of Ca substitution by Fe on the thermoelectric properties of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> ceramics

(Ca_1-xFe_x)₃Co₄O₉ polycrystalline samples (x?=?0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.1 and 0.2) have been prepared by solid state reaction and sintered by spark plasma sintering. Their thermoelectric properties have been studied between 323 and 1000 K. The substitution limit is low (< 3%). For higher iron contents, formation of Co₃O₄, Ca₂FeCoO₅ and a calcium ferrite compound occurs. Concerning electrical conductivity and power factor, an optimum value exists for x?=?0.03 substitution. This optimum power factor is circa 10% higher than the one of the unsubstituted sample. The optimum thermal diffusivity is measured for the sample with x?=?0.02 and is circa 9% lower than the one of the unsubstituted sample. Therefore, the dimensionless figure of merit ZT is finally increased by 14% for the (Ca_0.98Fe_0.02)₃Co₄O₉ and (Ca_0.97Fe_0.03)₃Co₄O₉ compositions.     

An iron-based T 1 contrast agent made of iron-phosphate complexes: In vitro and in vivo studies

A new iron-based T ₁ contrast agent consisting of a complex of iron ions coordinated to phosphate and amine ligands (Fe_(phos) in short) has been characterized by spectroscopic and magnetic measurements. NMR relaxation studies showed r ₁ values to be dependent on the phosphate salt concentration, K₂HPO₄, present in the medium. r ₁ reaches a maximum value of 2.5 mM^?1 s^?1 for measurements carried out at 7 T and 298 K. ³¹P MRS, Mössbauer spectroscopy and magnetic measurements of Fe_(phos) solutions suggest paramagnetic Fe³⁺ ions present in the studied iron–phosphate complex. In vitro and in vivo toxicity experiments with C6 cells and CD1 mice, respectively, demonstrated lack of toxicity for Fe_(phos) at the highest dose tested in the MRI experiments (12 mM iron for C6 cells and 0.32 mmol iron/kg for mice). Finally, T ₁ weighted images of brain tumours in mice have shown positive contrast enhancement of Fe_(phos) for tumour afflicted regions in the brain.     

Thermoelectric properties of Bi3+ substituted Co-based misfit-layered oxides

Highly densified (Ca_1?x Bi _x )₃Co₄O₉ thermoelectric ceramics with a layered structure were prepared by a sol–gel method followed by spark plasma sintering (SPS). Thermoelectric (TE) properties of the complex oxide ceramics were measured from room temperature to 700 °C. The results show that Bi³⁺ substitution leads to an increase in both electrical conductivity and Seebeck coefficient simultaneously. Bi³⁺ doped samples also show a lower thermal conductivity than undoped samples. The dimensional figure of merit ZT value of (Ca_0.95 Bi_0.05)₃Co₄O₉ samples is 0.25 at 700 °C.     

Effect of Temperature on the Elastic and Anelastic Behaviour of Magneto-Ferroelectric Composites Ba0.8Pb0.2TiO3 + Ni0.93Co0.02Mn0.05Fe1.95O4-δ in the Ferroelectric Rich Region

Composites with composition xBa_0.8Pb_0.2TiO₃+ (1 –x) Ni_0.93Co_0.02Mn_0.05Fe_1.95O_4- in which x varies as 1.0, 0.9, 0.7 and 0.5 in molar percent have been prepared by the conventional ceramic double sintering process. The presence of the two phases has been confirmed by X-ray diffraction. These composites were prepared for their use as magnetoferrolectric devices. Variation of longitudinal modulus (L) and internal friction loss (Q ^–1) of these samples with temperature at 142 kHz has been studied in the wide temperature range 300 to 630 K. The elastic behaviour (L) showed a break at the ferroelectric Curie temperature (498 K) in the case of pure ferroelectric material (Ba_0.8Pb_0.2TiO₃). This break shifted to lower temperature side as the ferrite component increases in the composite. The temperature variation of internal friction loss (Q ^–1) showed a corresponding stress induced relaxation peak at the ferroelectric-non-ferroelectric phase transition. This behaviour is explained in the light of structural phase transition.     

Magnetic properties of Ni-Zn ferrites prepared by microwave sintering method

The effect of zinc ion substitution for nickel on structural and magnetic properties of NiZn ferrites is reported. The spinel ferrite system Ni_1-xZn_xFe₂O₄ with x = 0.2, 0.3, 0.4 and 0.5 was prepared by microwave sintering method. The uniaxially pressed samples were sintered at various temperatures such as 900°C, 1000°C and 1100°C for 30 min. X-ray diffraction patterns of the samples indicate the formation of single-phase cubic spinel structure. SEM micrographs show that grain size increases with increasing zinc content and sintering temperature. The elemental composition of these ferrites was analyzed by EDS. Lattice constant increases with increase in zinc content, obeying Vegard’s law. The effect of composition and sintering temperature on initial permeability as the function of frequency and temperature was studied. The initial permeability of NiZn ferrite increases greatly with increasing Zn content and sintering temperature. The dependence of initial permeability with respect to temperature shows the decrease in the Curie point with increase in zinc content, is the normal behavior of ferrites. The relative loss factor (tand

In situ formation of sol-gel derived PbTiO3/NiFe2O4 biphase thin film

In this article, magnetoelectric (ME) biphase composite thin films consisted of PbTiO₃ as ferroelectric phase and NiFe₂O₄ as ferromagnetic phase which were successfully formed in situ by sol-gel process. The phase structure, morphology and dielectric properties of the films were measured by X-ray diffraction (XRD), scanning electron microscope (SEM) and LCR precision impedance analyzer. It is concluded that the thin films were capable of being controlled to form the biphase composite of PbTiO₃ and NiFe₂O₄ at the heat-treatment temperature between 600 and 850 °C. The phases coexisting in the composite thin film are in forms of solid solutions doped with Ni²⁺ and Fe³⁺ and with Ti⁴⁺, respectively. Their lattice constants vary with their doping contents. The capacitance of the composite thin film depends on the content of perovskite phase and the doping addition of Ni²⁺ and Fe³⁺ in crystalline phase of PbTiO₃.     

Effect of doped Ni2+ on the dielectric properties of NiO-BaTiO3 composites

NiO-BaTiO₃ composites were prepared by sintering BaTiO₃ together with NiO in air at 1300°C. Microstructure and morphology of the composites were detected by XRD and SEM, and the dielectric properties were measured by LCZ meter. The results indicate that the perovskite phase is formed in fact in status of solid solution doped with Ni²⁺, although only a small amount of Ni ions can dissolve into the perovskite phase. Ni doping decreases the formation temperature of the composite without inhibiting the grain growth of the crystalline phase. The dielectric constant decreases sharply and the dielectric loss decreases smoothly with increasing Ni²⁺ below NiO addition of 0.5 wt.%. When NiO addition increases above 0.5 wt.%, the dielectric constant and loss correlate with mixing rule of the two phases. Meanwhile, the replacement of Ni²⁺ for Ti⁴⁺ decreases the Curie temperature of perovskite phase by 30°C.