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Pure and Mg-substituted AgCaVO4 compounds were explored using the conventional solid-state sintering method and their microwave dielectric properties were investigated. The XRD patterns indicate all samples belong to an orthorhombic structure with a space group of Pmna. The pure AgCaVO4 ceramic gives the dielectric properties: εr of 11.7, Q × f of 15,000 GHz, and τf of38 ppm/°C at 530 °C. The value of τf is correlated with the bond valence. In a limited range (x = 0.03–0.05), a small amount of Mg substitution can not only reduce the dielectric loss, but also increase the dielectric constant of the AgCa1−xMgxVO4 specimen. AgCa0.97Mg0.03VO4 ceramic sintered at 530 °C exhibits optimum properties of εr = 12, Q × f = 23,000 GHz and τf = –35 ppm/°C at microwave frequencies. The ceramic also shows good chemical compatibility with aluminum, providing a promising candidate for ULTCC applications. [ABSTRACT FROM AUTHOR]

TiO2 ceramics synthesized from the rutile TiO2 powders with a mean size of ~ 0.4 μm were sintered at temperatures ranging from 500 to 1300 °C. The diffraction peaks matched well with the pure rutile phase. Grain growth is an important factor of densification and it becomes significant at 800–1300 °C, suggesting that the sintering process likely moves into the intermediate stage. The density renders a value of 97.5% at 1300 °C and starts to bend suggesting that the sintering is reaching its final stage. A thermostable and wide process window can be achieved for TiO2 specimen sintered at 500–800 °C, and it exhibits an εr of 21.7–28.18.8, a Q × f of 11,700–14,600 GHz, a τf of 383–390 ppm/°C, respectively. Not only did it provide a large positive τf, the rutile-TiO2 also rendered a stable and wide process window, suggesting that the proposed TiO2 ceramic can be a promising candidate for use as a τf compensator for ultra-low-temperature co-fired ceramics (ULTCC) materials and the microwave dielectric properties of ULTCC + TiO2 ceramics may be predictable through the mixing rules. [ABSTRACT FROM AUTHOR]

The present study systematically invesitgates the formation and microwave dielectric properties of novel AgMgVO 4 ceramics fabricated via the solid-state reaction method. The crystal structure of the ceramics is confirmed to be orthorhombic with a space Group of Pnma (62). A high relative density of 96.2% and an excellent combination of microwave dielectric properties with ε r of ~14.89, Q × f of ~19,400 GHz, and τ f of ~ − 2.71 ppm/°C can be achieved for the ceramic sintered at 630 °C. The dielectric constant is mainly influenced by the relative density (porosity) and dielectric polarizability. The Q × f is controlled by the microstructure, packing fraction, and lattice energy, which are also highly related to the unit-cell volume. A smaller unit-cell volume leads to a high Q × f. Variation of the τ f is strongly correlated to the bond valence of the specimen. Furthermore, the ceramic exhibits good chemical compatibility with aluminum electrodes and is demonstrated as a potent substrate for a band-pass filter with a center frequency of 3.5 GHz. These findings show a great promise for ultra-low temperature co-fired ceramic applications at high frequencies. [ABSTRACT FROM AUTHOR]

SrCo1-xMgxV2O7 (x = 0–0.09) dielectrics were prepared via the solid state route and the effect of Mg substitution on the microwave dielectric properties of the ceramics was systematically investigated. In addition to the relative density and microstructure, the dielectric polarizability, packing fraction, lattice energy and bond valence also play a crucial role in controlling the dielectric properties of the ceramics at microwave frequencies. A high lattice energy representing a high structural stability leads to a low dielectric loss in the specimen. Fluctuated variation of the τf was highly related to the bond valence of the samples. Specimens with x = 0.07 at 660°C revealed the highest Q × f of 23,000 GHz along with an εr of 13.2 and a τf of – 95 ppm/°C and it is chemically compatible with the Al electrode, suggesting that the dielectric is highly promising for ULTCC applications. [ABSTRACT FROM AUTHOR]

Novel Li 1−2x M x VO 3 (M = Mg, Zn) (x = 0–0.09) microwave dielectrics suitable for ULTCC (ultra-low temperature co-fired ceramics) applications were synthesized. The X-ray diffraction patterns revealed that all samples were monoclinic structured with a space group of C2/c. Microstructures, lattice parameters, and Raman spectra of the ceramics were also studied. Q × f (Q : quality factor) was mainly controlled by intrinsic and extrinsic loss, while the variation of τ f (temperature coefficient of resonant frequency) was related to ceramic bond valence. Poor microwave dielectric properties of pure LiVO 3 can be tremendously enhanced by substituting a minute amount of Mg or Zn in place of Li. Excellent properties could be obtained for specimens sintered at 520 °C with an ε r of 9.78, a Q × f of 45,600 GHz and an τ f of –45 ppm/°C for Li 0.98 Mg 0.01 VO 3 , in addition to an ε r (dielectric constant) of 9.25, a Q × f of 33,100 GHz and an τ f of –53.6 ppm/°C for Li 0.98 Zn 0.01 VO 3. Furthermore, the Li 0.98 Mg 0.01 VO 3 specimen was found to be chemically comparable with the Al electrode. With 2 mol% of TiO 2 added, the specimen at 520 °C achieved excellent characteristics which include an ε r of 9.2, a Q × f of 30,000 GHz, and an τ f of –2.8 ppm/°C, making it a very promising ULTCC dielectric for high-frequency 5 G applications. [ABSTRACT FROM AUTHOR]

The feasibility of novel LiCo1-xAxVO4 (A = Mg, Zn; x = 0–0.09) microwave dielectrics for ULTCC (ultra-low temperature co-fired ceramics) applications was investigated. Continuous solid solutions were formed as expected in the whole composition range and can be indexed in the cubic system with the Fd3m space group. The Raman spectrum of the specimen was also analyzed. All samples can be sintered into dense ceramics (relative density> 97%) at the temperature 650°C. The variation of structure parameters resulted from minutely substituting Co with Mg or Zn has significant effect on the microwave dielectric properties of the specimen. The relative density and dielectric polarizability have significant impact on the ɛr of the specimens. Q × f value is dominated by the density and packing fraction of the ceramics. The τf, however, was mainly controlled by the bond-valence of the samples under a minute substitution. Specimen with 0.01 mol% Zn-substitution at 650°C revealed the highest Q × f of 53,000 GHz along with an εr of 13.2 and a τf of – 57.5 ppm/°C. It also exhibited a good Al-cofiring chemical compatibility. [ABSTRACT FROM AUTHOR]

Novel ultra-low firing (Mg1-xZnx)V2O6(x = 0–0.09) ceramics have been investigated and systematically designed as promising dielectrics for ultra-low temperature co-fired ceramics applications. The X-ray diffraction patterns indicated that all samples crystallized in a monoclinic structure with a space group of C2/m. Microstructures and lattice parameters are presented and correlated with the microwave dielectric properties of the ceramics. The MgV2O6 specimen can be well-sintered at 610°C, the resulting ceramic of which featured an εr ~ 8.8, a Q × f ~ 10,300 GHz and a τf ~ – 29.7 ppm/°C. The tunable τf value can be adjusted to near zero along with a great promotion in the Q × f of MgV2O6 by using a small Zn substitution. In addition, excellent microwave dielectric properties (εr ~ 9.3, Q × f ~ 15,300 GHz @15.5 GHz and τf ~ – 3.4 ppm/°C) were obtained for the (Mg0.93Zn0.07) V2O6specimen sintered at 610°C for 4 h. The specimen is chemically compatible with Al electrodes and could be an ideal ultra-low temperature co-fired ceramics dielectric. Possible applications include the 5 G system, particularly with high frequency regions. [ABSTRACT FROM AUTHOR]

A novel low-loss and ultra-low temperature sinterable microwave dielectric material, AgZnVO 4 , was systematically investigated for the first time. The material exhibited a monoclinic structure with a space group P21/n, obtained by conventional solid-state processing. The material also showed combined microwave dielectric properties of ε r = 10.3, Q×f = 42,000 GHz, and τ f = –9.2 ppm/°C for specimens sintered at 540 °C. The partial substitution of Mg for Zn in the Ag(Zn 1−x Mg x)VO 4 ceramics effectively improved the densification and reduced the dielectric loss of the ceramics. X-ray diffraction patterns revealed a single solid solution phase of Ag(Zn 1−x Mg x)VO 4. The relative density, dielectric polarizability, packing fraction, lattice energy, and bond valence of the samples were calculated. An excellent combination of the microwave dielectric properties was obtained for Ag(Zn 0.97 Mg 0.03)VO 4 ceramic sintered at 540 °C: ε r = 10.6, Q×f = 52,000 GHz, and τ f = –10 ppm/°C. Additionally, the ceramic exhibited good chemical compatibility with aluminum electrodes, indicating great potential for ultra-low temperature co-fired ceramics (ULTCC) applications, particularly in the microwave and millimeter wave regions. • First systematic investigation of low-loss, ultra-low temperature sinterable AgZnVO 4 microwave dielectric. • AgZn 0.97 Mg 0.03 VO 4 ceramic at 540°C achieved optimized dielectric properties: ε r = 10.6, Q × f = 52,000 GHz, and τ f = –10 ppm/°C. • It showed great chemical compatibility with aluminum during co-firing, indicating promise for ULTCC applications. • A 5G millimeter wave patch antenna was designed for the AZMV ceramic. [ABSTRACT FROM AUTHOR]

This study investigates the microwave dielectric properties of pure CoMoO4 ceramics prepared using the conventional solid-state reaction method. Sintering temperatures ranging from 600° to 720°C were employed, and the effects of partial substitution of Mg2 + on these properties, specifically the sintering temperature and microwave dielectric characteristics, were examined. X-ray diffraction patterns revealed the formation of a single solid solution of Co1-xMgxMoO4 (x = 0–0.09) with a monoclinic structure and space group C2/m. Pure CoMoO4 samples sintered at 690 oC displayed dielectric properties of εr = 8.27, Q×f = 64,000 GHz, and τf = –96 ppm/°C. The partial substitution of Co2 + with Mg2 + effectively enhanced the densification of ceramics and reduced their dielectric loss and sintering temperature, which was systematically investigated with respect to dielectric polarization, lattice energy, packing fraction, and bond valence. The Co0.95Mg0.05MoO4 ceramic sintered at 630 oC exhibited excellent dielectric properties with εr = 8.42, Q×f = 71,000 GHz, and τf = –62.27 ppm/°C, and demonstrated good chemical compatibility. Furthermore, this ceramic was employed as a substrate for a 4 × 4 dual-polarized array antenna, indicating significant potential for use in ULTCC applications, particularly in the high-frequency millimeter wave region. [ABSTRACT FROM AUTHOR]

Li 2(1–x) M x WO 4 (M = Mg, Zn; x = 0.01–0.09) ceramics with an ultra-low sintering temperature of 540 °C were prepared by solid-state synthesis and their structural characteristics and microwave dielectric properties were systematically investigated. By replacing Li with 0.05 mol% Mg or 0.07 mol% Zn, the sintering temperature of the Li 2 WO 4 dielectric could be brought down from 660 to 540 °C along with the combined dielectric properties of the ε r of 6.2 and 5.8, a Q × f of 76,000 and 68,000 GHz, and the τ f of −94 and −86 ppm/°C, respectively. The corrected dielectric constant was found to be proportional to the ratio of α D (dielectric polarizability)/V m (molecular volume). The results showed that the Q × f values could be dramatically improved by increasing the density, packing fraction and lattice energy. Moreover, the τ f values of ceramics render a similar variation tendency by shifting linearly toward zero as the V cation increases. The Li 2(1–x) M x WO 4 ceramic is a glass-free, phase pure, and energy-saving dielectric ideal for ULTCC applications. [ABSTRACT FROM AUTHOR]

Ultra-low-firing-temperature ceramics (Mn 1−x Mg x)V 2 O 6 (x = 0–1) were prepared using the conventional solid-state reaction method. The effects of the Mn:Mg ratio on the crystal structure and microwave dielectric properties of the prepared ceramics were systematically investigated. The results indicated that an appropriate Mn:Mg ratio effectively improves the dielectric properties of the compounds. Specimens with x = 0.01 and x = 0.93 sintered at 630 °C exhibited the following microwave dielectric properties: ε r = 12.4 and 9.8, high Q×f = 57,000 and 21,000 GHz, and τ f = –15 and −24 ppm/°C, respectively. This suggests that the (Mn 0.99 Mg 0.01)V 2 O 6 ceramic is a potential material for ULTCC applications. [ABSTRACT FROM AUTHOR]

In this work, transparent amorphous- MgNb2 O6 thin films were fabricated on ITO/glass substrates using the sol-gel method. The change in the chemical states, as well as the optical and dielectric properties of MgNb2 O6 films at various annealing temperatures is investigated. In this study, MgNb2 O6 films exhibited the amorphous phase when the annealing temperature was below 600°C. From X-ray photoelectron spectroscopy, the major parts of the films' chemical states can be indexed as Mg2+, Nb5+, Nb4+, and O2−. Furthermore, the Nb4+ element can be reduced at higher annealing temperatures. The average transmission percentage in the visible range (λ = 400-800 nm) is over 80% for all MgNb2 O6/ ITO/glass samples, whereas the optical band gap ( Eg) for all samples is estimated at ~4 eV. In addition, the dielectric constant was calculated to be higher than 20 under a 1 MHz AC electric field, with a leakage current density below 2 × 10−7 A/cm2 at 1 V. In this study, the fabrication procedure and experiment results of MgNb2 O6 films are introduced for transparent microelectronics. [ABSTRACT FROM AUTHOR]

Abstract: (Mg1−x Zn x )1.8Ti1.1O4 (x =0.03–1.00) ceramics were prepared via the conventional solid-state method and their dielectric properties were investigated in the microwave frequency region. Formation of solid solutions was confirmed by the X-ray diffraction analysis, the EDX analysis, and the measured lattice parameters. A small amount of Zn substitution for Mg produced a large increase in Q × f due to a high packing fraction as well as a high relative density of the ceramics. By increasing x from 0.00 to 0.06, the Q × f of the specimen could be tremendously improved from 141,000 to a maximum of 210,700GHz (at 10.52GHz), demonstrating an unique potential for low-loss microwave applications. The τ f values were found to retain in the range from −54.2 to −62.3ppm/°C for all compositions because the resultant change of unit cell volume was small. Also, a remarkable lowering of the sintering temperature down to ∼300°C was observed when Mg was totally substituted by Zn, thereby making it possible for low firing applications. [Copyright &y& Elsevier]

Abstract: The (Mg0.95M0.05)Ta2O6 (M=Ni, Zn, Mn) ceramics are prepared through the solid-state ceramic route and their microwave dielectric properties are investigated as a function of ionic radius difference of M and Mg. The forming of (Mg0.95M0.05)Ta2O6 solid solutions were confirmed by the XRD analysis and the measured lattice parameters and the ceramics showed a nonlinear variation of dielectric properties with the sintering temperature. In addition, the sintering temperature has slight effect on dielectric constant and temperature coefficient of resonant frequency, but significant on Q×f value. In particularly, (Mg0.95Ni0.05)Ta2O6 shows a relatively high Q×f of 88,300 GHz along with a dielectric constant of 28.73 and a τ f of 44.9 ppm/°C, indicating the dielectric can be used for high-frequency applications. [Copyright &y& Elsevier]

The microwave dielectric properties of the (1 − x)( Mg0.95Ni0.05) TiO3- x( Ca0.8Sr0.2) TiO3 ceramic system prepared by mixed oxide route have been investigated. The crystal structures and the microstructures of the ceramics were characterized by means X-ray and scanning electron microscopy. The microwave dielectric properties are strongly related to the density and matrix of the specimen. Combination of ( Mg0.95Ni0.05) TiO3 (ilmenite-type structure) and ( Ca0.8Sr0.2) TiO3 (perovskite-structured) forms a two-phase system and leads to a near-zero temperature coefficient (τf). With increasing x, the quality factor ( Q × f) decreased and dielectric constant (εr) increased. A new microwave dielectric material 0.95( Mg0.95Ni0.05) TiO3-0.05( Ca0.8Sr0.2) TiO3, possessing excellent microwave dielectric properties with a dielectric constant (εr) of 21.68, a quality factor ( Q × f) of 94,000 (GHz) and a temperature coefficient (τf) of approximately −5.2 ppm/°C at 1275°C for 4 h, is proposed as a suitable candidate material for microwave applications requiring low dielectric loss. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric properties and the microstructures of the (1–x)MgTiO3–x(Ca0.8Sr0.2)TiO3 ceramic system prepared by the conventional solid-state route were investigated. (Ca0.8Sr0.2)TiO3 was employed as a τ f compensator and was added to MgTiO3 to achieve a temperature-stable material. Ilmenite-structured MgTiO3 and perovskite-structured (Ca0.8Sr0.2)TiO3 were coexisted and the two-phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the ε r of the specimen could be boosted by increasing amount of (Ca0.8Sr0.2)TiO3, it would instead render a decrease in the Q×f. The τ f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, τ f could be adjusted to a near-zero value by mixing 94mole% MgTiO3 and 6mole% (Ca0.8Sr0.2)TiO3. A dielectric constant (ε r ) of 21.42, a high Q×f value of 83,700GHz (at 9GHz) and a temperature coefficient of resonant frequency (τ f ) of −1.8ppm/°C were obtained for 0.94MgTiO3–0.06(Ca0.8Sr0.2)TiO3 sintered at 1300°C for 4h. It is proposed as a low-loss and low-cost dielectric material for microwave and millimeter wave applications. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric properties of the (1− x)(Mg0.95Co0.05)2TiO4–xCa0.8Sm0.4/3TiO3 ceramic system prepared by mixed oxide route have been investigated. The crystal structures and the microstructures of the ceramics were characterized by means of X-ray and SEM, respectively. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. Combining (Mg0.95Co0.05)2TiO4 (spinel structure) and Ca0.8Sm0.4/3TiO3 (perovskite structure) forms a two-phase system and leads to a near-zero τ f . With increasing x, the Q × f of the specimen decreased, whereas its ɛ r increased due to a compositional variation. A new microwave dielectric 0.8(Mg0.95Co0.05)2TiO4–0.2Ca0.8Sm0.4/3TiO3, possessing excellent microwave dielectric properties with a dielectric constant (ɛ r ) of 20.84, a Q × f of 112,600GHz (where f =9.1GHz, is the resonant frequency) and a τ f value ∼0.8ppmK−1 at 1573K/4h, is proposed as a candidate material for GPS patch antennas and 3G passive components. [Copyright &y& Elsevier]

The microwave dielectric properties of a (1− x)(Mg0.95Ni0.05)TiO3– xSrTiO3 ceramics system were investigated. The system was prepared using a conventional solid-state ceramic method. To produce a temperature-stable material, SrTiO3 was added, which led to a near-zero temperature variation in resonant frequency. The variation in microwave dielectric properties of the (1− x)(Mg0.95Ni0.05)TiO3– xSrTiO3 ceramics system significantly depends on the amount of SrTiO3 present. As x was varied from 0.01 to 0.1, the microwave Q× f value decreased from 105,000 to 31,000 GHz and the dielectric constant (ℇr) increased from 18.74 to 26.5. A microwave dielectric material with a dielectric constant (ℇr) of 21, a Q× f value of 73,000 GHz, and a τf value of 1 ppm/°C were obtained from the compound 0.96(Mg0.95Ni0.05)TiO3–0.04SrTiO3 sintered at 1300°C for 4 h. To verify the performance of the 0.96(Mg0.95Ni0.05)TiO3–0.04SrTiO3 ceramics, a band-pass filter with traditional hairpin resonators was designed and simulated on different dielectric materials [such as FR4, alumina, and 0.96(Mg0.95Ni0.05)TiO3–0.04SrTiO3]. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Nd0.5Na0.5TiO3 addition on the microwave dielectric properties of Mg0.95Ni0.05TiO3 ceramics was investigated. The Nd0.5Na0.5TiO3 content plays a significant role in improving the dielectric properties. Microwave dielectric measurements show an increase in the dielectric constant (εr ) and temperature coefficient of the resonant frequency (τf ) and a decrease in the quality factor (Q × f value) with increasing Nd0.5Na0.5TiO3 content. By properly adjusting the Nd0.5Na0.5TiO3 content, a zero τf value can also be obtained, which make Mg0.95Ni0.05TiO3 a promising material in wireless systems. At 1300°C, the 0.81Mg0.95Ni0.05TiO3–0.19Nd0.5Na0.5TiO3 ceramics possess excellent microwave dielectric properties: a dielectric constant (εr ) of 25.61, a Q × f value of 69,100GHz, and a τf value of −6ppm/°C. [Copyright &y& Elsevier]

Abstract: Low-loss ceramics in the (1− x)(Mg0.95Zn0.05)2TiO4–xSrTiO3 system have been prepared by the conventional mixed oxide route and their microwave dielectric properties have been investigated. A two-phase system was confirmed by the XRD patterns, the EDS analysis and the measured lattice parameters. The addition of SrTiO3, having a smaller grain size in comparison with that of (Mg0.95Zn0.05)2TiO4, could effectively promote the densification in the (Mg0.95Zn0.05)2TiO4 matrix. The specimen using 0.94(Mg0.95Zn0.05)2TiO4–0.04SrTiO3 sintered at 1270°C possesses an excellent combination of microwave dielectric properties: ɛ r of ∼18, Q × f of ∼125,600GHz (at 10GHz), and τ f of ∼0ppm/°C. The dielectric is proposed as a candidate material for low-loss microwave and millimeter wave applications. [Copyright &y& Elsevier]

Abstract: The microwave dielectric properties and the microstructures of the (1− x)(Mg0.95Co0.05)TiO3–x(Na0.5Nd0.5)TiO3 (0.1≤ x ≤0.18) ceramic system have been investigated. The two phase system was confirmed by XRD and EDX analysis throughout the entire experimental range. In this system, the microwave dielectric properties can be effectively controlled by varying the x value. The dielectric constant ranged from 18.3 to 25.4 as the x varies from 0.1 to 0.18. With the increase of sintering temperature, the Q × f increased to a maximum and decreased thereafter. A maximum Q × f ∼112,000GHz (where f =8.6GHz, is the resonant frequency) was achieved for samples with x =0.1. For practical applications, a new microwave dielectric material, 0.84(Mg0.95Co0.05)TiO3–0.16(Na0.5Nd0.5)TiO3, is suggested and possesses a good combination of dielectric properties: ɛ r ∼24.39, Q × f ∼70,000GHz, τ f ∼1.6ppm/°C. It is proposed as a suitable candidate dielectric for GPS patch antennas and passive components in wireless communication system. [Copyright &y& Elsevier]

Abstract: The microstructures and microwave dielectric properties of the (1− x)(Mg0.95Ni0.05)TiO3–xCa0.8Sm0.4/3TiO3 ceramics system were investigated in the range of 0.1≦ x ≦0.9. The quality factor (Q × f value) and the temperature coefficient (τ f ) of the specimens were decreased with increasing Ca0.8Sm0.4/3TiO3 content. The microstructures of (1− x)(Mg0.95Ni0.05)TiO3–xCa0.8Sm0.4/3TiO3 ceramics were characterized using X-ray diffraction patterns and a scanning electron microscope (SEM). The areas of the various compositions in the ceramics were observed using energy dispersive spectroscopy (EDS), showing that Ca0.8Sm0.4/3TiO3 coexists with (Mg0.95Ni0.05)TiO3 in minor crystal grain. The existence of the Ca0.8Sm0.4/3TiO3 phase can inhibit the abnormal grain growth of the (Mg0.95Ni0.05)TiO3 phase. A relative permittivity (ɛ r) of 22.9, a Q × f value of 92,000GHz, and temperature coefficient of resonant frequency (τ f ) of −5.4ppm/°C were obtained for 0.9(Mg0.95Ni0.05)TiO3–0.1Ca0.8Sm0.4/3TiO3 ceramics sintered at 1275°C for 4h. [Copyright &y& Elsevier]

Abstract: The microstructures and the microwave dielectric properties of the (1− x)Mg0.95Co0.05TiO3 − xZn0.975Ca0.025TiO3 ceramic system prepared using the conventional solid state method were investigated. In order to achieve a temperature-stable material, a method of combining a positive temperature coefficient material with a negative one studied. Zn0.975Ca0.025TiO3 has dielectric a constant ɛ r ∼30, Q × f value∼45,000GHz, and a large positive τ f value∼30ppm/°C. Mg0.95Co0.05TiO3 has a high dielectric constant (ɛ r ∼16.8), high quality factor (Q × f value∼230,000 at 10GHz), and a negative τ f value (−54ppm/°C). The dielectric constant decreased from 29.1 to 18.36 when x changed from 0.9 to 0.3. In the x(Mg0.95Zn0.05Ti)O3 −(1− x)Zn0.975Ca0.025TiO3 system, the microwave dielectric properties can be effectively controlled by varying the x value. At 1200°C, 0.7Mg0.95Co0.05TiO3 −0.3 Zn0.975Ca0.025TiO3 had a dielectric constant (ɛ r ) of 22.6, a Q × f value of 57,000GHz, and a temperature coefficient of resonant frequency (τ f ) of 0ppm/°C. [Copyright &y& Elsevier]

Composite ceramics in a solid solution of (Mg1− x Mn x)2TiO4 ( x=0.02–0.1) have been prepared by the mixed oxide route. Formation of the solid solution was confirmed by the X-ray diffraction, the EDX analysis, and the measured lattice parameters, which varied linearly from Mg2TiO4 ( a= b= c=8.4410 Å) to (Mg0.9 Mn0.1)2TiO4 ( a= b= c=8.4445 Å). The XRD analysis also confirmed the co-existence of a cubic-structured (Mg1− xMn x)2TiO4 and an ilmenite-structured second phase (Mg1− xMn x)TiO3. The composition expected to have a maximum Q× f (276 200 GHz at 10.5 GHz) is (Mg0.95Mn0.05)2TiO4 with ℇr∼15.69 and τf∼−52.6 ppm/°C. The existence of the second phase, however, would lead to no significant variation in the dielectric properties of the specimen because it possesses compatible properties compared with that of the main phase. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ZnO addition on the microstructures and microwave dielectric properties of 0.96Mg0.95Co0.05TiO3–0.04SrTiO3 ceramics were investigated. ZnO was selected as liquid phase sintering aids to lower the sintering temperature of 0.96Mg0.95Co0.05TiO3–0.04SrTiO3 ceramics. With ZnO additives, the densification temperature of 0.96Mg0.95Co0.05TiO3–0.04SrTiO3 can be effectively reduced from 1450°C to 1250–1350°C. The crystalline phase exhibited no phase difference at low addition levels (0.5–4wt%). It is found that low-level doping of ZnO (0.5–4wt%) can significantly improve the density and dielectric properties of 0.96Mg0.95Co0.05TiO3–0.04SrTiO3 ceramics. The quality factors Q × f was strongly dependent upon the amount of additives. Q × f values of 74,000GHz and 30,000GHz could be obtained at 1250–1350°C with 1wt% and 4wt% ZnO additives, respectively. During all additives ranges, the relative dielectric constants were not significantly different and ranged from 20.1 to 27.77. The temperature coefficient varies from −8ppm/°C to 2.7ppm/°C. [Copyright &y& Elsevier]

Abstract: The microwave dielectric properties of the (1− x)(Mg0.95Co0.05)TiO3–xCa0.6La0.8/3TiO3 ceramic system prepared by mixed oxide route have been investigated. The crystal structures and the microstructures of the ceramics were characterized by means of X-ray and SEM. The microwave dielectric properties are functions of the sintering temperature as well as the composition. Alternation of phases between ilmenite-type structure and pseudo-cubic perovskite crystal is observed. The 0.9(Mg0.95Co0.05)TiO3–0.1Ca0.6La0.8/3TiO3 ceramics possesses excellent microwave dielectric properties with a dielectric constant ɛ r of 21.86, a Q × f value of 131,000GHz (at 7GHz) and a τ f value of −15.5ppm/°C at 1350°C/4h. It is proposed as a suitable material candidate for applications requiring low microwave dielectric loss. [Copyright &y& Elsevier]

Abstract: The effects of B2O3 additives on the microstructures and the microwave dielectric properties of complex perovskite 0.66Ca(Mg1/3Nb2/3)O3–0.34CaTiO3 ceramics were investigated. The B2O3 additives, acting as a sintering aid, can effectively lower the sintering temperature of the ceramics to as low as 1200°C. No second phase was observed throughout the entire experiments. Moreover, boron was not found in the grains but residual at the boundaries indicating a liquid phase sintering. At 1250°C, the 0.25wt% B2O3-doped 0.66Ca(Mg1/3Nb2/3)O3–0.34CaTiO3 ceramics possesses a relative permittivity ɛ r of 43.94, a Q × f value of 30,000GHz (measured at 6.7GHz) and a τ f value of −1.9ppm/°C. It exhibits a substantial temperature reduction (>200°C) and compatible dielectric properties in comparison with that of un-doped one. [Copyright &y& Elsevier]

Abstract: The effects of additive sintering aids on the microstructures and microwave dielectric properties of 0.8(Mg0.95Zn0.05)TiO3-0.2Ca0.61Nd0.26TiO3 ceramics were investigated. B2O3 was selected as a liquid phase sintering aid to lower the sintering temperature of 0.8(Mg0.95Zn0.05)TiO3-0.2Ca0.61Nd0.26TiO3 ceramics. With added B2O3, the densification temperature of 0.8(Mg0.95Zn0.05)TiO3-0.2Ca0.61Nd0.26TiO3 can be effectively reduced from 1350°C to 1125–1250°C. Low-level doping of B2O3 (0.5–4wt.%) significantly improves the density and dielectric properties of 0.8(Mg0.95Zn0.05)TiO3-0.2Ca0.61Nd0.26TiO3 ceramics. The quality factor Q × f was strongly dependent upon the amount of additives. Q × f values of 21200 and 54900GHz could be obtained at 1125–1250°C with 0.5 to 4wt.% B2O3 added, respectively. Over all ranges of addition, the relative dielectric constants differed significantly and ranged from 24.1 to 26.6. The temperature coefficient varied from 2.9 to 10.03ppm/°C. [Copyright &y& Elsevier]

Abstract: Ceramics in the system (1− x)(Mg0.95Zn0.05)TiO3–x(Na0.5Nd0.5)TiO3 were prepared by the conventional mixed oxide route. It shows a two-phase system of an ilmenite structured (Mg0.95Zn0.05)TiO3 and a perovskite structured (Na0.5Nd0.5)TiO3, which were confirmed by XRD and EDX. In addition, (Mg0.95Zn0.05)Ti2O5 was identified as a second phase. It was also responsible for a rapid drop in the Q × f value. The temperature coefficient of resonant frequency was a function of compositional ratio. Specimen with x =0.16 possessed an excellent combination of microwave dielectric properties: ε r ~24.27, Q × f ~82,000 GHz (at 9 GHz) and τ f ~0 ppm/°C. [Copyright &y& Elsevier]

Abstract: The microstructures and the microwave dielectric properties of the x(Mg0.95Zn0.05)TiO3–(1− x) Ca0.8Sm0.4/3TiO3 ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca0.8Sm0.4/3TiO3 has dielectric properties of dielectric constant εr ~ 120, Q × f value ~13,800 GHz and a large positive τ f value ~400 ppm/°C. (Mg0.95Zn0.05)TiO3 possesses high dielectric constant (ε r ~16.21), high quality factor (Q × f value ~210,000 at 9 GHz) and negative τ f value (−59 ppm/°C). Sintering at 1300 °C with x =0.9, 0.9(Mg0.95Zn0.05Ti)O3 −0.1 Ca0.8Sm0.4/3TiO3 has a dielectric constant (ε r) of 22.7, a Q × f value of 124,000 GHz and a temperature coefficient of resonant frequency (τ f ) of −6.3 ppm/°C. [Copyright &y& Elsevier]

Abstract: The microstructures and the microwave dielectric properties of the x(Mg0.95Zn0.05)TiO3–(1− x)Ca0.61Nd0.26TiO3 ceramic system prepared by conventional solid state method were investigated. In order to achieve a temperature-stable material, two compounds with negative and positive temperature coefficients were employed to form a mixed phases. With partial replacement of Mg by Zn, dielectric properties of the x(Mg0.95Zn0.05)TiO3–(1− x)Ca0.61Nd0.26TiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. An excellent Q × f value of 130,000GHz can be obtained for the system with x =0.9 at 1300°C. For practical application, a dielectric constant (ɛ r) of 24.3, a Q × f value of 112,000GHz and a temperature coefficient of resonant frequency (τ f) of −10.1ppm/°C for 0.85(Mg0.95Zn0.05Ti)O3–0.15Ca0.61Nd0.26TiO3 at 1300°C is proposed in this paper. [Copyright &y& Elsevier]

The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 (NCT) ceramics using starting powders of Nd2O3, CoO, and TiO2 prepared by the conventional solid-state route have been researched. The dielectric constant values (ℇr) saturated at 24.8–27. Quality factor ( Q× f) values of 37 900–140 000 (at 9 GHz) and the measured τf values ranging from −45 to −48 ppm/°C can be obtained when the sintering temperatures are in the range of 1410°–1500°C. The ℇr value of 27, the Q× f value of 140 000 (at 9 GHz) and the τf value of −46 ppm/°C were obtained for NCT ceramics sintered at 1440°C for 4 h. For applications of high selective microwave ceramic resonator, filter, and antenna, NCT is proposed as a suitable material candidate. [ABSTRACT FROM AUTHOR]

Abstract: Crystal structure and the microwave dielectric properties of xMgTiO3–(1−x)MgTa2O6 sintered specimens with x =0.3, 0.5, 0.7 are investigated. The X-ray diffraction patterns revealed the sintered specimens are mixed phases of MgTiO3, MgTa2O6 and MgTi2O5. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. With x =0.7, a new microwave dielectric ceramic material 0.7MgTiO3–0.3MgTa2O6 at 1460°C for 3h is suggested for microwave device and it possesses excellent dielectric properties; a dielectric constant ɛ r ∼23, a Q × f value ∼81,000GHz and a τ f value ∼−2ppm/°C. The correlation between microwave dielectric properties and the microstructures is also discussed. [Copyright &y& Elsevier]

The microwave dielectric properties and the microstructures of Sm(Co1/2Ti1/2)O3 ceramics with B2O3 additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B2O3 (up to 0.5 wt%) can effectively promote the densification of Sm(Co1/2Ti1/2)O3 ceramics with low sintering temperature. It is found that Sm(Co1/2Ti1/2)O3 ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B2O3 addition. At 1,290 °C, Sm(Co1/2Ti1/2)O3 ceramics with 0.5 wt% B2O3 addition possess a dielectric constant ( ε r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of −11.4 ppm/ °C. The B2O3-doped Sm(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B2O3 (up to 0.75wt.%) can significantly improve the density and dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics. Nd(Co1/2Ti1/2)O3 ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320°C. Second phases were not observed at the level of 0.25–0.75wt.% B2O3 addition. The temperature coefficient of resonant frequency (τ f ) was not significantly affected, while the dielectric constants (ɛ r) and the unloaded quality factors Q were effectively promoted by B2O3 addition. At 1320°C/4h, Nd(Co1/2Ti1/2)O3 ceramics with 0.75wt.% B2O3 addition possesses a dielectric constant (ɛ r) of 27.2, a Q × f value of 153,000GHz (at 9GHz) and a temperature coefficient of resonant frequency (τ f ) of 0ppm/°C. The B2O3-doped Nd(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. [Copyright &y& Elsevier]

Abstract: The microstructures and the microwave dielectric properties of the (1− x)(Mg0.95Co0.05)TiO3–xCa0.6La0.8/3TiO3 ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca0.6La0.8/3TiO3 has dielectric properties of dielectric constant ε r ∼109, Q × f value∼17,600GHz and a large positive τ f value∼213ppm/°C. (Mg0.95Co0.05)TiO3 ceramics possesses high dielectric constant (ε r ∼16.8), high quality factor (Q × f value∼230,000GHz), and negative τ f value (−54ppm/°C). As the x value varies from 0.1 to 0.8, (1− x)(Mg0.95Co0.05)TiO3–xCa0.6La0.8/3TiO3 ceramic system has the dielectric properties as follows: 21.55< ε r <75.44, 21,000< Q × f <90,000 and −10< τ f <140. By appropriately adjusting the x value in the (1− x)(Mg0.95Co0.05)TiO3–xCa0.6La0.8/3TiO3 ceramic system, zero τ f value can be achieved. With x =0.15, a dielectric constant ε r ∼25.78, a Q × f value∼84,000GHz (at 9GHz), and a τ f value∼2ppm/°C were obtained for 0.85(Mg0.95Co0.05)TiO3–0.15Ca0.6La0.8/3TiO3 ceramics sintered at 1400°C for 4h. For practical application in communication systems, it is desirable to be able to sinter at lower temperatures. Therefore, V2O5 was as a sintering aid for lowering the sintering temperature of0.85(Mg0.95Co0.05)TiO3–0.15Ca0.6La0.8/3TiO3 ceramics. At the same time, the 0.85(Mg0.95Co0.05)TiO3–0.15Ca0.6La0.8/3TiO3 ceramic system with 0.5wt% V2O5 can be obtained good properties at the microwave frequencies for 1200°C. [Copyright &y& Elsevier]

Abstract: The microwave dielectric properties of conventional solid state route prepared 0.95Ba(Zn1/3Ta2/3)O3–0.05BaZrO3 ceramics with CuO addition have been investigated. Ordering structure was not observed at sintering temperatures 1280–1430°C. Copper oxide, as a sintering aid, was found to effectively lower the sintering temperature of 0.95Ba(Zn1/3Ta2/3)O3–0.05BaZrO3 ceramics. The Q × f values of 58000–93000 (at 7GHz) can be obtained when the sintering temperatures are in the range of 1280–1430°C. The permittivity (ɛ r ) as well as the temperature coefficient of resonant frequency τ f was strongly correlated to the CuO content but independent of the sintering temperature. The ɛ r value of 29.6, Q × f value of 93000 (at 7GHz) and τ f value of 3.1ppm°C−1 were obtained for 0.95Ba(Zn1/3Ta2/3)O3–0.05BaZrO3 ceramics with 1wt.% CuO addition sintered at 1430°C for 4h. For applications of high selective microwave ceramic resonator and filter, 0.95Ba(Zn1/3Ta2/3)O3–0.05BaZrO3 is proposed as a suitable material candidate. [Copyright &y& Elsevier]

Abstract: The crystal structures and the microwave dielectric properties of the xSrTiO3–(1− x)Ca(Mg1/3Nb2/3)O3 perovskite ceramic system have been investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. SrTiO3 has dielectric properties of dielectric constant ε r ∼205, Q × f value ∼4200 GHz and a large positive τ f value ∼1700 ppm/°C. Ca(Mg1/3Nb2/3)O3 possesses high dielectric constant (ε r ∼28), high quality factor (Q × f value ∼58,000 at 7 GHz) and negative τ f value (−48 ppm/°C). As the x value varies from 0.2 to 0.8, the xSrTiO3–(1− x)Ca(Mg1/3Nb2/3)O3 system has the dielectric properties as follows: 40< ε r <123, 4600< Q × f <33,400 and −23< τ f <600. A new microwave dielectric material, 0.3SrTiO3–0.7Ca(Mg1/3Nb2/3)O3, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε r ∼46, a Q × f value ∼29,300 GHz (at 6.8 GHz) and a τ f value ∼−2 ppm/°C. A near-zero τ f value can be achieved by adjusting the x value of xSrTiO3–(1− x)Ca(Mg1/3Nb2/3)O3 ceramics. [Copyright &y& Elsevier]

Abstract: The effects of sintering aid addition on the microstructures and microwave dielectric properties of La(Mg1/2Ti1/2)O3 ceramics were investigated. CuO was selected as liquid phase sintering aid to lower the sintering temperature of La(Mg1/2Ti1/2)O3 ceramics. With CuO addition, the densification temperature of La(Mg1/2Ti1/2)O3 can be effectively reduced from 1600 to 1300–1500°C. It is found that doping of CuO (1–4wt%) can significantly improve the density and dielectric properties of La(Mg1/2Ti1/2)O3 ceramics. Second phases were observed at the level of 1–4wt% CuO additions. The quality factor Qxf was strongly dependent upon the amount of additions. Qxf values of 33,800 and 10,600GHz could be obtained at 1300–1500°C with 1 and 4wt% CuO addition, respectively. During all addition ranges, the relative dielectric constants were different and ranged from 25.89 to 29.63. The temperature coefficient varies from −52.11 to −68.22ppm/°C. [Copyright &y& Elsevier]

Abstract: Effect of DC biasing field on the real part of the relative dielectric constant of (Ba0.6Sr0.4)TiO3 and ZrO2-doped (Ba0.6Sr0.4)TiO3 for application in phased array antennas have been characterized. The composites have adjustable dielectric properties. The grain size is maximum for (Ba0.6Sr0.4)TiO3 doped with 0.5 wt.% ZrO2 content. The real part of the relative dielectric constant of the specimens decreases with increasing applied DC biasing field. The tunability and grain size have similar trends as a function of ZrO2 contents. The tunability of the real part of the relative dielectric constant for (Ba0.6Sr0.4)TiO3 doped with 0.5 wt.% ZrO2 content is about 45.74% and 45.88% at 20 and 40 MHz, respectively. [Copyright &y& Elsevier]

This study investigated the correlation of sintering effects on piezoelectric properties of Nb modified lead zirconate titanate (PZT) piezoceramics produced by the conventional solid reaction sintering. Samples were prepared at a composition Zr/Ti=53/47, contiguous to a morphotropic phase boundary (MPB) for 1 mol% Nb2O5. Replacement of Ti+4 by Nb+5 in such perovskite type solid solutions was accomplished by the creation of cation vacancies. These created vacancies seemed to facilitate material transport and benefit sintering. Calcined at 850 °C/2 h and sintered at 1250 °C/2 h, the PZT ceramics yielded a minimum value of the mechanical quality factor (Qm) 50, and exhibited a maximum electromechanical coupling factor κp 0.62, in accordance with the relationship between the mechanical quality factor and electromechanical coupling factor. In addition, during the sintering process a piezoelectric charge constant at d33 was found to be of 385 pC/N. It was noted that the fundamental resonance frequency was around 200 kHz, which was suitable for piezoelectric nebulizer (fluid atomizer), ultrasonic cleaning transducer applications. [Copyright &y& Elsevier]

The effects of CuO addition on the microstructures and microwave dielectric properties of ZnTa2O6 ceramics were investigated. CuO was selected as a liquid-phase sintering aid to lower the sintering temperature of ZnTa2O6 ceramics. With CuO addition, the sintering temperature of ZnTa2O6 can be effectively reduced from 1350 to 1230 °C. The crystalline phase exhibited no phase difference and no second phase was detected at low addition levels (0.25–1 wt.%). The quality factors Q × f were strongly dependent upon the CuO concentration. A Q × f value of 65,500 GHz was obtained for specimen with 0.25 wt.% CuO addition at 1230 °C. For all levels of CuO concentration, the relative dielectric constants were not significantly different and ranged from 34.2 to 35.7. Tunable temperature coefficient of resonant frequency (τf) can be adjusted to zero by appropriately turning the CuO content. [Copyright &y& Elsevier]

The microwave dielectric properties and the microstructures of 0.5LaAlO3–0.5SrTiO3 ceramics with CuO addition prepared with conventional solid-state route have been investigated. Doping with CuO (up to 1 wt.%) can effectively promote the densification and remain comparable dielectric properties of 0.5LaAlO3–0.5SrTiO3 ceramics. It is found that 0.5LaAlO3–0.5SrTiO3 ceramics can be sintered at 1400 °C due to the sintering aid effect resulted from CuO as addition observed by scanning electron microscopy. The dielectric constant as well as the Q×f value decreases with increasing CuO content. At 1460 °C, 0.5LaAlO3–0.5SrTiO3 ceramics with 0.25 wt.% CuO addition possess a dielectric constant (#x03B5;r) of 35.2, a Q×f value of 24 000 (at 8 GHz) and a temperature coefficient of resonant frequency (τf) of -13.5 ppm/°C. [Copyright &y& Elsevier]

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg1/3Ta2/3)O3 exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V2O5 (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg1/3Ta2/3)O3 ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V2O5 addition. The detected second phase Ta2O5 was mainly the result of V5+ substitution in the ceramics. Dielectric constant (&epsiv;r) and temperature coefficient of resonant frequency (τf) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V2O5 addition due to the increase in B-site ordering. The &epsiv;r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τf value of 7.2 ppm/°C were obtained for Ba(Mg1/3Ta2/3)O3 ceramics with 0.25 wt.% V2O5 addition sintered at 1500 °C for 3 h. [Copyright &y& Elsevier]

The influence of sintering effects on microstructure, mechanical quality factor Qm and electromechanical coupling factor κ of 1 mol% Nb-doped lead zirconate titanate (PZT) piezoceramics with a composition Zr/Ti=53/47 prepared by the conventional ceramic technology were investigated. Replacement of Ti+4 by Nb+5 in such perovskite type solid solutions was accomplished by the creation of cation vacancies. These created vacancies seemed to facilitate material transport and benefit from sintering. Calcined at 850 °C/2 h and sintered at 1250 °C/2 h, the PZT ceramics had the minimum value of Qm 50 and exhibited maximum electromechanical coupling factor κp 0.62 in accordance with the relationship between mechanical quality factor and electromechanical coupling factor. The measured P–E hysteresis loop illustrated that the remanent polarization (Pr) and coercive field (Ec) were 8.63 μC/cm2 and 17.2 kV/cm, respectively. The fundamental resonance frequency was around 200 kHz, which was suitable for piezoelectric resonator and filter applications. [Copyright &y& Elsevier]

The microwave dielectric properties of conventional solid-state route prepared 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 ceramics have been investigated. Ordering structure was not observed at sintering temperatures 1350–1500 °C. The dielectric constant values (&epsiv;r) saturated at 40–41. BaZrO3 was found to effectively promote the Q×f value of Ba(Zn1/3Nb2/3)O3 ceramics. The Q×f values of 15,000–96,000 (at 7 GHz) can be obtained when the sintering temperatures are in the range of 1350–1450 °C. The temperature coefficient of resonant frequency τf was a function of sintering temperature. The &epsiv;r value of 42, Q×f value of 96,000 (at 7 GHz) and τf value of 27 ppm/°C were obtained for 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 ceramics sintered at 1450 °C for 2 h. For applications of high selective microwave ceramic resonator and filter, 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 is proposed as a suitable material candidate. [Copyright &y& Elsevier]

The microwave dielectric properties and the microstructures of the (1−x)MgTiO3–xCaTiO3 ceramic system were investigated. With partial replacement of Mg by Co, dielectric properties of the (1−x)(Mg0.95Co0.05)TiO3–xCaTiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature. At 1275°C, the 0.95(Mg0.95Co0.05)TiO3–0.05CaTiO3 ceramics possesses excellent microwave dielectric properties: a dielectric constant &epsiv;r of 20.3, a Q×f value of 107 000 ( at 7 GHz) and a τf value of −22.8 ppm/°C. By appropriately adjusting the x value in the (1−x)(Mg0.95Co0.05)TiO3–xCaTiO3 ceramic system, zero τf value can be achieved. With x=0.07, a dielectric constant &epsiv;γ of 21.6, a Q×f value of 92 000 (at 7 GHz) and a τf value of −1.8 ppm/°C was obtained for 0.93(Mg0.95Co0.05)TiO3–0.07CaTiO3 ceramics sintered at 1275°C for 4 h. [ABSTRACT FROM AUTHOR]

Ba2−xSm4+2x/3Ti9O26 (x=0–0.3) was selected as the formula for BaO–Sm2O3–4.5TiO2 ceramics based on the structure formula of the tungsten–bronze-type structure. The microstructure and microwave dielectric properties of Ba2−xSm4+2x/3Ti9O26 and the relationships between them were investigated in this study. The microstructure of Ba2−xSm4+2x/3Ti9O26 ceramics consists of a uniform matrix of primary BaO–Sm2O3–4TiO2 and BaO–Sm2O3–5TiO2 with small amounts of dispersed second phase, TiO2 and Ba2Ti9O20. Excellent dielectric properties of &epsiv;r=68–79, Q×f=11 000–12 500 GHz and good temperature stability at the resonant frequency (τf=0 ppm per °C) were obtained. The relationships between the microstructure, second phases and microwave dielectric properties were concerned. XRD patterns, energy dispersive X-ray spectrometer (EDS) analysis and scanning electron microscopy are also presented. [Copyright &y& Elsevier]