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.     

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.     

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.     

Microstructure and Physical Characteristics of Novel Z-Type Hexaferrite with Cu Modification

The influence of Cu modification of physical characteristics of Co₂Z hexaferrites, which have stoichiometric compositions of Ba₃Co_{2(1 – x)}Cu_2x Fe₂₄O₄₁ (x 0.50), was investigated. The results show that the microstructure of modified hexaferrites is improved greatly. In the range of solid solubility of Cu, the cell parameters (a and c) of Co₂Z hexaferrites with Cu modification show a reverse change, a of hexagonal parameter decreases and c of axial parameter increases. The saturation magnetization, remnant magnetization, hysteresis behavior, initial permeability and quality factor as well as its possible affecting factors of Cu modified Co₂Z hexaferrites are also discussed in this paper.     

Dielectric properties and morphotropic phase boundaries in the xPb(Zn1/3Nb2/3)O3−(1−x)Pb(Zr0.5Ti0.5O3 pseudo-binary system

Ceramics in the xPb(Zn_1/3Nb_2/3)O₃−(1−x)Pb(Zr_0.5Ti_0.5)O₃ [xPZN–(1−x)PZT] solid solution system are expected to display excellent dielectric, piezoelectric, and ferroelectric properties in compositions close to the morphotropic phase boundary (MPB). The dielectric behavior of ceramics with x = 0.1−0.6 has been characterized in order to identify the MPB compositions in this system. Combined with X-ray diffraction results, ferroelectric hysteresis measurements, and Raman reflectivity analysis, it was consistently shown that an MPB exists between x = 0.2 and x = 0.3 in this binary system. When x ≤ 0.2, the tetragonal phase dominates at ambient temperatures. In the range of x ≥ 0.3, the rhombohedral phase dominates. For this rhombohedral phase, electrical measurements reveal a profound frequency dispersion in the dielectric response when x ≥ 0.6, suggesting a transition from normal ferroelectric to relaxor ferroelectric between 0.5 ≤ x ≤ 0.6. Excellent piezoelectric properties were found in 0.3PZN–0.7PZT, the composition closest to the MPB with a rhombohedral structure. The results are summarized in a PZN–PZT binary phase diagram.     

Evaluating voltage-tunable materials for RF phase shifter technology

Abstract

Today's phased-array antennas use hundreds of radiating elements that use relatively high-loss phase shifters that operate over a limited bandwidth. The number of elements and the phase shifter losses affect the overall cost of the antenna system. Ferroelectric RF phase shifters have the potential to meet the low-loss, low-cost requirements driving many phased-array applications. Some of the issues affecting the development of ferroelectric phase shifters include ferroelectric tunability, dielectric losses, conductor losses, and impedance mismatch. We used the measured tunability (250 kHz, room temperature), dielectric constant, and loss tangent (10 GHz, room temperature) of Ba_1-xSr_x/TiO₃ (0.4x 0.6) with various amounts of MgO additive, 0 to 60 wt.%, to estimate the device performance of microstrip phase shifters. The electromagnetic model of the microstrip (which uses a standard 3-mil-wide 1-oz. copper line, 3-mil-thick BST/MgO composite and the bias criteria of 2 V/μm) has produced performance benchmarks for a number of composites providing 360° of phase shift. While the accuracy of the electromagnetic model used to evaluate these materials has limitations, the results do provide some insight as to which materials may be better suited for 10-GHz phase shift devices.     

Dielectric,ferroelectric and ferromagnetic properties of x Ni0.8Zn0.2Fe2O4-(1-x) Pb0.99La0.02Zr0.65Ti0.35O3 composites

For the present study, two phase ceramic (ferroelectric-ferrite) composites using La substituted lead zirconate titanate (PLZT) and Ni-Zn ferrite (NZF) with compositional formula x Ni_0.8Zn_0.2Fe₂O₄-(1-x) Pb_0.99La_0.02Zr_0.65Ti_0.35O₃ (x?=?0, 0.05, 0.10 and 0.15) were synthesized by conventional solid state reaction route. From X-ray analysis, it was confirmed that no chemical reaction took place between individual phases. Dielectric properties were studied as a function of temperature and frequency. Decrease in dielectric constant and increase in dielectric loss was observed with increasing ferrite content. Anomalous behavior in paraelectric region was observed for all the composite samples (x?=?0.05, 0.10 and 0.15) at low frequencies. To study ferroelectric and ferromagnetic properties, P-E and M-H hysteresis loops were recorded respectively. Effect of electric field on magnetization was studied for all composite samples to confirm magnetoelectric coupling.     

YBa2Cu3O7-x/SrTiO3//LaAlO3 heterostructures obtained by injection MOCVD

Abstract

YBa₂Cu₃O_7-x /Ba_xSr_1-xTiO₃ /LaAlO₃ heterostructures can be used as a basis for devices with voltage control in microwave circuits.

Ba_xSr_1-xTiO₃ (x=0–0.1) (BST) thin films have been epitaxially grown on LaAlO₃ substrates using injection MOCVD. The excellent crystalline quality of the obtained BST films can be proven by a FWHM of <0,2° for the rocking curve of the (002) BST reflection. An AFM study revealed flat surfaces, showing a surface roughness R_s as low as 1nm. YBa₂Cu₃O_7-x/Ba_xSr_1-x TiO₃//LaAlO₃ heterostructures were than optimised. The YBa₂Cu₃O_7-x (YBCO) layers obtained on Ba_xSr_1-xTiO₃ films are epitaxial with a FWHM of 0.45° for the (005) YBCO rocking curve and display very promising superconducting properties of T_c=92K.

Finally the microwave properties of the superconducting films were studied. For YBa₂Cu₃O_7-x layers directly deposited on LaAlO₃, surface resistance values of 0,32mΩ were obtained, while for YBa₂Cu₃O_7-x /SrTiO₃//LaAlO₃ heterostructures, higher values of 1mΩ at 8.5GHz were measured.     

Dielectric Behavior and Magnetoelectric Effect in Ni0.75Co0.25Fe2O4 + Ba0.8Pb0.2TiO3 ME Composites

Magnetoelectric composites with ferrite + ferroelectric compositions xBa_0.8Pb_0.2TiO₃ + (1 – x) Ni_0.75Co_0.25Fe₂O₄ in which x varies as 0, 0.55, 0.70, 0.85 and 1.0 were prepared by ceramic method. X-ray analysis confirms single-phase formation in x = 0 and x = 1 compositions, whereas the presence of both phases is shown in x = 0.55, 0.70 and 0.85 compositions. Variation of dielectric constant () with temperature and frequency has been studied. All the samples have show linear magnetoelectric conversion in the presence of static magnetic field. Static magnetoelectric conversion factor, (dE/dH), was measured as a function of magnetic field in the samples with x = 0.55, 0.70 and 0.85 compositions. The maximum value of dE/dH was found to be 140 V/cm/Oe for x = 0.85 composition.     

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.     

Dielectric and Mechanical Losses in (Ba,Sr)TiO3 Systems

In the application of tuneable microwave devices of ferroelectric (BaSr)TiO₃ systems the two critical parameters needed for optimal device performance are high tunability and low dielectric loss. The dielectric loss of the materials is strongly dependent on microstructure. This paper is concerned with an investigation of the variation in the dielectric and mechanical losses in Ba _x Sr_{1 – x} TiO₃ systems (x = 0.5, 0.6, 0.7 and 1.0) with microstructure (grain sizes from 1 m to 50 m). The magnitude of the loss peak and sharpness of the anomaly in the dielectric constant/elastic modulus observed for the phase transitions in Ba _x Sr_{1 – x} TiO₃, depend not only on the composition and but also on the grain size. A relaxation peak has been observed in large grain material, which is indication of interactions between different configurations of domain walls and the diffusion of oxygen vacancies in the domains.     

Preparation, thermal stability and permeability behavior of substituted Z-type hexagonal ferrites for multilayer inductors

Co₂Z-type hexagonal ferrites with iron excess Ba₃Co_2???x Fe_24?+?x O₄₁ (0?≤?x?≤?0.8) and deficiency Ba₃Co_2?+?y Fe_24???y O₄₁ (0?≤?y?≤?0.6) were prepared by an oxalate coprecipitation technique. This synthesis route leads to almost single phase Z-type ferrites for x?=?0 after calcination and sintering at 1330 °C. The Z-type formation is enhanced for x?>?0 and single phase ferrites are obtained for 0.4?≤?x?≤?0.8. The permeability of Z-type ferrites varies with composition x: Maximum permeability of μ′?=?28 is observed for 0.4?≤?x?≤?0.6 for samples sintered at 1330 °C. The frequency dispersion shows broad peaks of μ″ stretching from 200 MHz to >1 GHz. For iron deficient samples 0?≤?y?≤?0.6 multi-phase mixtures were obtained. For Ag-based multilayer inductor applications sintering at 950 °C is required. Co₂Z ferrites with Fe excess are not stable at this temperature as demonstrated by XRD. The permeability of samples sintered at 950 °C is drastically reduced to μ′?=?3. This demonstrates that these materials are not able to provide sufficient permeability for multilayer inductors for high-frequency operations since they are not compatible with the low temperature ceramic cofiring technology.     

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.     

Ferroelectric effect in spin coated Ba0.9Sr0.1TiO3 thin films

Abstract

The achievement of excellent growth of lead zirconium titanate (PZT) films by various techniques for use as ferroelectric memories has generated an extensive research interest in the synthesis of various other perovskite and layered oxides. Ba_xSr_1?xTiO₃ thin films have also been deposited by various methods to study their dielectric behavior. We report the synthesis of Ba_xSr_1?xTiO₃ (where x ' 0.9, 0.1) by a solution method using hydroxides, acetates, and nitrate salts as precursors for barium and strontium, and titanium isopropoxide for titanium. The films deposited by spin coating on ITO coated glass substrates showed ferroelectric behavior.     

Structural and magnetic properties of Ba0.98Zn0.02Ti1-xMnxO3 ceramics

Our paper reports the influence of Mn doping on structural, magnetic and electrical properties of Ba_0.98Zn_0.02Ti_1-xMn_xO₃ ceramics (here x?=?0.04, 0.06, 0.08). Structural and magnetic properties are significantly modified by changing Mn ion concentration at Ti site. With the increase in Mn ion concentration (x?≥?0.04), structural phase transition occurs from tetragonal to hexagonal. Magnetization hysteresis loop is broaden and enhanced magnetization is observed with increase in Mn ion concentration. This enhanced magnetic effect is likely to originate from exchange interactions between different oxidation states of Mn ions. All compositions showed ferroelectric behavior. It clearly enumerates from our observations that magnetism especially ferromagnetism can be induced in the barium titanate ferroelectric ceramic with control of suitable substituents.     

Magnetic properties of ZnO-doped cobalt ferrite

The cobalt ferrites with chemical composition Co_1+x Zn _x Fe_2?2x O₄ (x?=?0.0, 0.1, 0.2, 0.4) were obtained with conventional solid reaction. The ZnO-doped samples have lower lattice constant than CoFe₂O₄ by adjusting Co ions to the octahedral sites. The results show that doping ZnO could extremely improve the magnetic properties. In comparison with pure CoFe₂O₄, the little ZnO-doped sample has higher permeability and much lower coercivity at the condition of a little decrease of magnetization saturation. Sample with x?=?0.1 shows evident magnetostrictive effect at the magnetic field of 30–60 mT while pure cobalt ferrite sample does not, though the saturation magnetostriction decreases. These indicate that ZnO-doping improves the magnetostrictive sensitivity of the cobalt ferrites and have potential applications in magnetoelectric devices and magnetic detector.     

Dielectric and relaxor ferroelectric properties of Ba-doped Pb(Zr,Ti)O3 ceramics

(Pb,Ba)(Zr,Ti)O₃ is a relaxor ferroelectric material. Dielectric and ferroelectric properties of (Pb_1-x Ba _x )(Zr_0.70Ti_0.30)O₃ ceramics have been investigated for compositions varying in the range of 0.20?≤?x?≤?0.30. Reagent grade PbO, ZrO₂, TiO₂ and BaCO₃ raw powders were used, ceramics were fabricated by convenient solid state reaction. The experimental results show that the substitution of Ba for Pb can enhance the ferroelectric relaxor characteristics. With the Ba content increasing, the electric hysteresis was narrowed and the polarization was reduced. Meanwhile the temperature T _m that corresponding to the maximal dielectric constant was decreased. It has also been found that the hydrostatic pressure may cause the phase transition more diffuse and move T _m to higher temperature.     

Structural and magnetic evolution of Fe-doped TiO<Subscript>2</Subscript> nanoparticles synthesized by sol-gel method

Nanocrystalline Ti_1-x Fe _x O₂ particles were fabricated via sol-gel method and their structures, morphology and magnetic properties were investigated. The structure of the Ti_1-x Fe _x O₂ nanospheres evolved from mixed anatase and rutile phases to pure anatase phase with increasing iron content. Additionally, it is found the evolution of magnetism: sample x = 3% shows room temperature ferromagnetism while the rests exhibit paramagnetism. The hysteresis loop of sample x = 3% is attributable to paramagnetic and ferromagnetic phase and the paramagnetic and ferromagnetic components are separated. The susceptibility of Ti_1-x Fe _x O₂ increases and then decreases with the increase of Fe content. The magnetism is explained by the BMP theory.     

Ni-Cu-Zn Ferrites for Low Temperature Firing: I. Ferrite Composition and its Effect on Sintering Behavior and Permeability

Ni-Cu-Zn ferrites of composition Ni_{1 − x − y}Cu_yZn_xFe₂O₄ with 0.4 ≰ x ≰ 0.6 and 0 ≰ y ≰ 0.25 were prepared by standard ceramic processing routes. The density of samples sintered at 900^∘C increases with copper concentration y. Dilatometry reveals a significant decrease of the temperature of maximum shrinkage with y. The permeability has maximum values of μ = 500–1000 for x = 0.6. The Curie temperature is sensitive to composition and changes form about 150^∘C for x = 0.6 to T_c > 250^∘C for x = 0.4, almost independent on the Cu-content. A small iron deficiency in Ni_0.20Cu_0.20Zn_{0.60 + z}Fe_{2 − z}O_{4 − (z/2)} with 0 ≰ z ≰ 0.06 significantly enhances the density of samples sintered at 900^∘C. The maximum shrinkage rate is shifted to T < 900^∘C. These compositions are therefore appropriate for application in low temperature co-firing processes. The permeability is reduced with z, hence a small z = 0.02 seems to be the optimum ferrite composition for high sintering activity and permeability.     

Structural and Initial Permeability Studies of Li-Zn-Co Ferrites

A series of cobalt substituted lithium zinc ferrites having the compositional formula Li_0.4–0.5xZn_0.2Co_xFe_2.4–0.5xO₄, where 0.00 ≤ x ≤ 0.1 in steps of 0.02, was prepared by the citrate precursor method. Structural studies on the prepared samples were carried out by using XRD and SEM measurements. Spinel phase structure of the samples was confirmed by XRD. From the XRD data the lattice parameter and the theoretical density were calculated. The experimental density was also determined using the Archimedes principle. Lattice parameter was observed to increase with increasing Co²⁺ ion concentration. The densification in both the cases, theoretical and experimental, shows an increase with composition. SEM studies carried out show that average grain diameter are in the range of 300 nm–650 nm and a fall is observed with increasing Co²⁺ ion content. The investigation on initial permeability as a function of composition and frequency were also undertaken. It is seen that there is decrease in the value of initial permeability with addition of Co content. The initial permeability and permeability loss show dispersion with frequency. Possible mechanisms contributing to the above processes are discussed.