Microwave dielectric properties of (Ca0.8Sr0.2)(SnxTi1−x)O3 ceramics

In this paper, we study the behavior of the B-site behavior with the incorporation of Sn⁴⁺ ion in (Ca_0.8Sr_0.2)TiO₃ ceramics. An excess of Sn⁴⁺ resulted in the formation of a secondary phase of CaSnO₃ and SrSnO₃ affecting the microwave dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics. The dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics were improved because of the solid solution of Sn⁴⁺ substitution in the B-site. The temperature coefficient of resonant frequency (τ_f) of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics also improved with increasing Sn content.     

Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

Microwave dielectric properties of BaCu2−xMnxSi2O7 (x = 0–0.04) ceramics

Journal of Materials Science: Materials in Electronics - BaCu2?xMnxSi2O7 (x?=?0–0.04) microwave dielectric ceramics were synthesized through solid-state reaction method....     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Microwave dielectric properties of doped Ba6−x(Sm1−y′Ndy)8+2x/3Ti18O54 oxides

Dielectric ceramic compositions for microwave applications belonging to the (BaO)-(Nd₂O₃)-(Sm₂O₃)-(TiO₂) phase diagram were studied. Two compositions were selected for study, the doping effect of MnO₂, WO₃, CaO on dilatometry, microstructure and microwave properties. The effect of the nature and the amount of dopants on microstructure and microwave properties were clearly demonstrated. The effect of the addition of 1 or 2wt% WO₃, MnO₂ and CaO to Ba₄ (Sm_0.6, Nd_0.4)_9.33Ti₁₈O₅₄ and Ba_3.75(Sm_0.5, Nd_0.5)_9.5Ti₁₈O₅₄ was studied. It was found that these two compositions lead to dense ceramics exhibiting excellent microwave properties, for instance =74–81, Q × f up to 9000 Ghz at 3 Ghz and _f around +9 p.p.m.°C^–1.     

Microwave dielectric properties and microstructures of Nd(Mg0.5?xCoxSn0.5)O3 ceramics

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5?xCo_xSn_0.5)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5?xCo_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.45Co_0.05Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (? _r ) of 19.2, a quality factor (Q?×?f) of 68,900?GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?67?ppm/°C were obtained for Nd(Mg_0.45Co_0.05Sn_0.5)O₃ ceramics that were sintered at 1,550?°C for 4?h.     

Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Microwave dielectric properties and microstructures of Ca(Nb1−xTax)2O6 ceramics

This study elucidates the microwave dielectric properties and microstructures of Ca(Nb_1?xTa_x)₂O₆ ceramics with a view to their potential for microwave devices. The Ca(Nb_1?xTa_x)₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Ca(Nb_0.93Ta_0.07)₂O₆ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (? _r ) of 17.7, a quality factor (Q × f) of 117,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?51 ppm/°C were obtained for Ca(Nb_0.93Ta_0.07)₂O₆ ceramics that were sintered at 1,400 °C for 4 h.     

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na_1/2Ln_1/2)TiO₃> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (_f) (where Ln represents a lanthanide: La⁺³, Pr⁺³, Nd⁺³ and Sm⁺³). On the other hand, MgTiO₃ ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO₃-(1 – x)(Na_1/2 Ln_1/2) TiO₃. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO₃ and Na_1/2 Ln_1/2)TiO₃ phases. Its dielectric characteristics (Q ^*f, temperature coefficient and dielectric constant) are intermediate between (Na_1/2 Ln_1/2) TiO₃ and MgTiO₃ and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q ^*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.     

Microwave dielectric properties of Ba[(Zn1−xCox)1/3Nb2/3]O3 ceramics

Microwave dielectric ceramics of Ba[(Zn_1−xCo_x)_1/3Nb_2/3]O₃ (x=0–0.8) were prepared by solid-state reaction method. The microwave dielectric properties, such as dielectric constants, Q×f values and τ_f (temperature coefficient of resonant frequency) were studied as a function of compositions and sintering temperatures. The results revealed that the dielectric constant and Q×f value decrease almost linearly with increasing x. With x increasing from 0 to 0.8, the dielectric constant decreases from 42 to 33, and Q×f value from 75,491 to 20,248 GHz. A nearly zero τ_f ceramic with dielectric constant of 33 and Q×f value of 20,248 GHz was obtained at x=0.8. The sintering temperature has slight effect on dielectric constant, but significant on Q×f value. The microstructures and crystal structures were characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis techniques to reveal the mechanisms.     

Microwave dielectric properties of (1 − x)(Mg0.4Zn0.6)2SiO4–xCaTiO3 composite ceramics

Phase formation, microstructure and microwave dielectric properties of (1 ? x)(Mg_0.4Zn_0.6)₂SiO₄–xCaTiO₃ (MZS-C) composite ceramics synthesized by using the conventional solid-state method were systematically investigated. Three phase structure was observed in all samples by using X-ray diffraction and the back scattering electron images. Mg₂SiO₄ can form a solid solution with Zn₂SiO₄, which improved sinterability of the MZS-C composite ceramics. As the CaTiO₃ content was increased from 0.06 to 0.14, dielectric constant ε _r and temperature coefficient of resonant frequency τ _f values of the MZS-C ceramics sintered at 1,180 °C for 4 h increased from 6.74 to 8.35 and ?41.5 to ?6.46 ppm/°C, respectively. Zero τ _f value can be obtained by properly adjusting the x value of the (1 ? x)MZS–xC ceramics. With increasing content of CaTiO₃, densification temperatures of the composite ceramics were decreased. The composite ceramic with x = 0.14 sintered at 1,180 °C for 4 h exhibited excellent microwave dielectric properties of ε _r = 8.35, Q × f = 28,125 GHz and τ _f = ?6.46 ppm/°C.     

Structural and dielectric relaxor properties of A-site deficient samarium-doped (Ba1−x Sm2x/3)(Zr0.3Ti0.7O3) ceramics

Rare earth samarium (Sm)-doped barium zirconate titanate (Ba_1?x Sm_2x/3)(Zr_0.3Ti_0.7)O₃ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed single-phase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M–O bonds. Raman spectroscopic study revealed that the substitution of Ba²⁺ ions by Sm³⁺ ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm³⁺ ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel–Fulcher relation.     

Synthesis and properties of dielectric (HfO2)1 − x (Sc2O3) x films

(HfO₂)_{1 ? x} (Sc₂O₃) _x films have been grown by chemical vapor deposition (CVD) using the volatile complexes hafnium 2,2,6,6-tetramethyl-3,5-heptanedionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptanedionate (Sc(thd)₃) as precursors. The composition and crystal structure of the films containing 1 to 36 at % Sc have been determined. The results demonstrate that, in the composition range 9 to 14 at % scandium, the films are nanocrystalline and consist of an orthorhombic three-component phase, which has not been reported previously. Using Al/(HfO₂)_{1 ? x} (Sc₂O₃) _x /Si test structures, we have determined the dielectric permittivity of the films and the leakage current through the insulator as functions of scandium concentration. The permittivity of the films with the orthorhombic structure reaches k = 42–44, with a leakage current density no higher than ～10^?8 A/cm².     

Synthesis and dielectric and nonlinear properties of BaTi1 − x Zr x O3 ceramics

We have studied the formation of BaTi_{1 ? x} Zr _x O₃ solid solutions with the perovskite structure. The phase composition, microstructure, and electrical properties of the BaTi_{1 ? x} Zr _x O₃ materials have been investigated. The results demonstrate that their dielectric permittivity (?) and loss tangent (tan δ) decrease with increasing zirconium content. At the same time, their nonlinearity coefficient (n ^R ) remains large (n _R = 30–50%) in relatively low fields (E = 30–50 kV/cm). The present data suggest that the materials studied here are potentially attractive for use in creating nonlinear devices of modern microelectronics.     

Microwave dielectric properties of Mg2SiO4–Ca1−ySm2y/3TiO3 composite ceramics

In this work, (1?x)Mg₂SiO₄–xCa_1?ySm_2y/3TiO₃ ceramics were fabricated using the conventional solid-state reaction method. When y?=?0.2, the effects of Ca_1?ySm_2y/3TiO₃ contents on microstructure, phase evolution, and microwave dielectric properties of the samples were studied. The X-ray diffraction showed that Mg₂SiO₄ and Ca_0.8Sm_0.4/3TiO₃ co-existed in composite ceramics. The dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) increased with the increasing content of Ca_0.8Sm_0.4/3TiO₃, while the quality factor (Q?×?f) decreased. At x?=?0.22, the (1?x) Mg₂SiO₄–xCa_0.8Sm_0.4/3TiO₃ ceramics sintered at 1325?°C for 3?h possessed optimal microwave dielectric properties: ε_r?~?11.89, Q?×?f value?~?32,703?GHz and τ_f?~?+?0.49?ppm/°C. As a result, the ε_r of (1?x) Mg₂SiO₄?+?xCa_1?ySm_2y/3TiO₃ ceramics could be adjusted in the range of 10.83 to 13.88 while the τ_f is near-zero.

     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.