Microwave Dielectric Properties Of Mg Research Articles

Structure, far-infrared spectroscopy, microwave dielectric properties, and improved low-temperature sintering characteristics of tri-rutile Mg 0.5Ti 0.5TaO 4 ceramics

In this study, tri-rutile type Mg_0.5Ti_0.5TaO₄ ceramics were synthesized, where the structure–property relationship, especially the structural configuration and intrinsic dielectric origin of Mg_0.5Ti_0.5TaO₄ ceramics, and the low-firing characteristics were studied. It is found that the tri-rutile structural type is unambiguously identified through the Rietveld refinement analysis, the selected area electron diffraction (SAED), and the high-resolution transmission electron microscopy (HRTEM) along the [110] zone axis. With the increase in sintering temperature, the densification and uniformity of crystal growth play important roles in regulating the microwave dielectric properties of Mg_0.5Ti_0.5TaO₄ ceramics. Intrinsically, theoretical dielectric properties calculated by the far-infrared reflective spectra approached the experimental values, indicating the importance of structural features to dielectric properties. Furthermore, a glass additive with high matching relevance with ceramics has been developed to decrease the high sintering temperature of Mg_0.5Ti_0.5TaO₄ ceramics, where 2–4 wt% Li₂O–MgO–ZnO–B₂O₃–SiO₂ (LMZBS) glass frit was adopted to reduce the suitable temperature from 1275 to 1050 ℃ without significantly deteriorating the microwave dielectric characteristics. Specifically, Mg_0.5Ti_0.5TaO₄ ceramics containing 2 wt% glass addition sintered at 1050 ℃ for 4 h possess excellent microwave dielectric properties: dielectric constant (<i>ε</i>_r) = 44.3, quality factor multiplied by resonant frequency (<i>Q</i>×<i>f</i>) = 23,820 GHz (<i>f</i> = 6.2 GHz), and the temperature coefficient of resonant frequency (<i>τ</i>_<i>f</i>) = 123.2 ppm/℃.

Effect of substituting Ti sites with (Mg Nb0.8-0.4)4+ on the microwave dielectric properties of Mg2TiO4 ceramics

Abstract The microwave dielectric properties of Mg 2 Ti 0.95 (Mg x Nb 0.8-0.4 x ) 0.05 O 4 (0 ≤ x ≤ 1) ceramics were investigated based on the structural characteristics obtained by Rietveld refinement. Specimens with 0 ≤ x ≤ 0.75 showed a single-phase inverse spinel structure with cubic symmetry. The average ionic radius increased with increase in x because of the larger ionic radius of Mg 2+ (0.72 A) than Nb 5+ (0.64 A). However, the lattice parameter decreased because of an increase in the bond valence of the Ti site, which in turn led to an increase in the packing fraction of the unit cell. The quality factor ( Qf ) of the specimens increased with increase in x up to x = 0.75 and then decreased because of the inclusion of secondary phases, such as MgTiO 3 and Mg-rich spinels. For single-phase specimens, the Qf value depended on the packing fraction of the unit cell. Despite the higher ionic polarizability of Nb 5+ (3.97 A) than Mg 2+ (1.32 A), the dielectric constants remained constant due to the increase of relative density of the specimens with x . The temperature coefficients of the resonant frequency of all the specimens were similar.

Microwave dielectric properties of Mg 4 Nb 2 O 9 -based ceramics with (B x W 1−x ) 5+ substitutions at Nb 5+ sites (B = Li, Mg, Al, Ti)

Abstract The dependences of the microwave dielectric properties on the isovalent substitution of (Li 1+ 1/5 W 6+ 4/5 ) 5+ , (Mg 2+ 1/4 W 6+ 3/4 ) 5+ , (Al 3+ 1/3 W 6+ 2/3 ) 5+ and (Ti 4+ 1/2 W 6+ 1/2 ) 5+ at the Nb 5+ -sites of Mg 4 Nb 2 O 9 ceramics were investigated. For the samples sintered at 1350 °C for 10 h, a single phase of corundum structure with hexagonal symmetry was observed through the entire range of compositions. The structural characteristics of the Mg 4 Nb 1.95 (B x W 1- x ) 0.05 O 9 ceramics were quantitatively evaluated by Rietveld refinement method from the X-ray diffraction data. The specimens containing (Ti 4+ 1/2 W 6+ 1/2 ) 5+ substitutions had the highest quality factor ( Qf ) of 233,000 GHz of all the samples. The dielectric constants ( K ) of the samples were similar for all compositions. The temperature coefficient of the resonant frequency ( TCF ) of the samples was dependent on the distortion of the oxygen octahedra (Δ avg × 10 3 ). As the distortion of the oxygen octahedra increased, the TCF values decreased and eventually become negative.

Low temperature and broadband dielectric properties of V2O5 doped Mg2TiO4 ceramics

The liquid phase effect of V(2)O(5) on the densification, microstructure and microwave dielectric properties of Mg(2)TiO(4) (MTO) ceramics has been investigated. The addition of V(2)O(5) significantly lowered the sintering temperature compared to pure MTO ceramics with improved microstructure, relative density and microwave dielectric properties. The increase in relative density and average grain size via growth of large grains and dissolution of small grains is explained by Ostwald ripening phenomena. Further, the microwave dielectric properties of the pure and MTO with V(2)O(5) samples were measured at cryogenic temperatures. It was observed that the loss tangent (tan ) and Q × f o of pure MTO increased with temperature, whereas the loss tangent and Q × f o of the samples with V(2)O(5) decreased with a rise in temperature. However, the MTO ceramics added with 0.5 and 1.0 wt% of V(2)O(5) manifested slightly higher loss tangents as compared to the pure MTO ceramics. The mechanism of the microwave loss is in agreement with the theory of intrinsic dielectric loss derived from the two phonon difference process. Further, the distinctive loss peak at 40 K is attributed to the orientation polarization having dispersion at the microwave frequency. The addition of V(2)O(5) did not cause any changes on the temperature stability of the MTO ceramics, whereas the temperature coefficient of the permittivity increases with an increase in temperature. The broadband dielectric measurement reveals that the V(2)O(5) doping increases the dielectric constant and enhances the stability over a wide frequency range, and shows a peak around 1.8 GHz. The tan of pure MTO still shows the peak whereas the samples doped with V(2)O(5) suppresses this peak significantly.

Influence of sintering temperature on dielectric properties and crystal structure of corundum-structured Mg4Ta2O9 ceramics at microwave frequencies

Abstract Microwave dielectric properties of corundum-structured Mg 4 Ta 2 O 9 ceramics were investigated as a function of sintering temperatures by an aqueous sol–gel process. Crystal structure and microstructure were examined by X-ray diffraction (XRD) technique and field emission scanning electron microscopy (FE-SEM). Sintering characteristics and microwave dielectric properties of Mg 4 Ta 2 O 9 ceramics were studied as a function of sintering temperature from 1250 °C to 1450 °C. With increasing sintering temperature, the density, e r and Qf values increased, saturating at 1300 °C with excellent microwave properties of e r =11.9, Qf =195,000 GHz and τ f =−47 ppm/°C. Evaluation of dielectric properties of Mg 4 Ta 2 O 9 ceramics were also analyzed by means of first principle calculation method and ionic polarizability theory.

Microwave dielectric properties of high-Q Mg(Sn x Ti1−x )O3 ceramics

A series of Sn-doped Mg(Sn x Ti1−x )O3 ceramics were prepared using the conventional solid-state route. The influence of Sn4+ substitution for Ti4+ on the microstructure and microwave dielectric properties of Mg(Sn x Ti1−x )O3 ceramics was systematically investigated. Substitution with a suitable amount of Sn can eliminate the MgTi2O5 phase. The dielectric constants and temperature coefficients of resonant frequency changed slightly with the variation in Sn content in the specimens. However, the quality factors (Q) dramatically improved and were sensitive to the concentration of Sn4+. The high Q value was attributed to the uniform grain, clean and narrow grain boundary, and elimination of the MgTi2O5 phase. Moreover, the composition-optimized Mg(Sn0.05Ti0.95)O3 ceramics sintered at 1390°C exhibited excellent microwave dielectric properties of ɛ r = 17.61, Q×f = 328,543 GHz, and τ f = −42 ppm/°C.

Correlation between Sn substitution for Ti and Microwave Dielectric Properties of Magnesium Titanate Ceramics

The relationship between Sn substitution for Ti and microwave dielectric properties of Mg(Ti1‐xSnx)O3 ceramics was investigated. Sn4+ could substitute for Ti4+ in MgTiO3 and increase the crystal volume. All samples exhibited the MgTiO3‐type phase with ilmenite structure as main phase. At the x range from 0 to 0.05, the secondary phase of Mg2TiO5 was observed. Upon further increasing Sn content up to 0.15, the SnO2 phase appeared. When the x value increased from 0 to 0.05, the dielectric constant decreased slightly and the quality factor increased sharply, whereas the dielectric constant increased and the quality factor decreased as the x value varied from 0.05 to 0.15. The temperature coefficient of resonant frequency moved toward positive value with Sn substitution. In particular, at the x range from 0.05 to 0.07, the ceramic sintered at 1360°C for 4 h exhibited excellent microwave dielectric properties of εr = 16.8–17.1, Qf = 298,000–312,000 and τf = −53~−50 ppm/°C.

Microwave dielectric properties of Mg(Zr0.05Ti0.95)O3-SrTiO3 ceramics

The microwave dielectric properties of (1−x)Mg(Zr0.05Ti0.95)O3-xSrTiO3 ceramics prepared by conventional solid processing were investigated. With increasing x, the dielectric constant and the quality factor decreased, and the temperature coefficient of resonant frequency was tuned from negative to positive value. The effect of sintering temperature on microwave properties was also studied. After sintering at 1,390 °C for 4 h, the ceramics exhibited a near zero temperature coefficient of resonant frequency about 2.1 ppm/°C, an optimum dielectric constant of 20.9 and a high quality factor of 203000 (6.8 GHz), at the level of x = 0.05.

Effect of CaTiO 3 addition on microwave dielectric properties of Mg 2(Ti 0.95Sn 0.05)O 4 ceramics

The microwave dielectric properties of CaTiO 3-added Mg 2(Ti 0.95Sn 0.05)O 4 ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg 2(Ti 0.95Sn 0.05)O 4 and perovskite-structured CaTiO 3 forms a two-phase system (1 − x)Mg 2(Ti 0.95Sn 0.05)O 4– xCaTiO 3, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ f . The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg 2(Ti 0.95Sn 0.05)O 4–0.09CaTiO 3 is suggested and it possesses a good combination of dielectric properties with an ɛ r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.

The effect CuO additive on the microwave dielectric properties of Mg(Zr 0.05Ti 0.95)O 3 ceramics

The microwave dielectric properties of the Mg(Zr 0.05Ti 0.95)O 3 ceramics with CuO addition were investigated. All specimens were prepared by solid-state reaction method and sintered at 1270–1420 °C for 4 h. When CuO was added, the second phases of MgTi 2O 5, TiO 2 and liquid phase were produced. Moreover, the Mg 0.25Zr 0.38Ti 0.38O 1.75 second phase has existed in pure Mg(Zr 0.05Ti 0.95)O 3 ceramics. The formation of second phases is accompanied by a significant decrease in dielectric loss and increase in density and τ f. For specimens with 1.5 wt% CuO sintered at 1300 °C, the dielectric constant, Q × f and τ f values were 18.2, 223,000 GHz and −2 ppm/°C, respectively.

Effect of sintering aid on microwave dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics

Abstract The effects of B 2 O 3 addition on the sintering behavior, microstructure, and the microwave dielectric properties of Mg(Zr 0.05 Ti 0.95 )O 3 (MZrT) ceramics have been investigated. The results of X-ray diffraction (XRD) indicate the presence of six crystalline phases, Mg(Zr 0.05 Ti 0.95 )O 3 , Mg 0.25 Zr 0.38 Ti 0.38 O 1.75 , Mg 2 TiO 4 , MgTi 2 O 5 , TiO 2 , and (Mg,Ti) 2 (BO 3 )O, in the sintered ceramics, depending on the amount of B 2 O 3 added. It was found that the firing temperature required to make the Mg(Zr 0.05 Ti 0.95 )O 3 ceramics dense is lowered by increasing the B 2 O 3 content. The τ f value of the Mg(Zr 0.05 Ti 0.95 )O 3 with B 2 O 3 glass was also improved dramatically. Addition of 1.5 wt% B 2 O 3 glass lowers the sintering temperature of Mg(Zr 0.05 Ti 0.95 )O 3 from 1420 to 1270 °C, with relatively high Q × f = 108,000 (GHz), ɛ r of 17.6, and of low τ f = −2 ppm/°C.

Effect of Li2CO3 Addition on the Sintering Temperature and Microwave Dielectric Properties of Mg2V2O7 Ceramics

Li2CO3 was added to Mg2V2O7 ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li2CO3 changed the crystal structure of Mg2V2O7 ceramics from triclinic to monoclinic. The 6.0 mol% Li2CO3‐added Mg2V2O7 ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛr=8.2, Q×f=70 621 GHz, and τf=−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li2CO3‐added Mg2V2O7 ceramic at 800°C. Therefore, this ceramic is a good candidate material in low‐temperature co‐fired ceramic multilayer devices.

Microwave dielectric properties of Mg 3(VO 4) 2– xBa 3(VO 4) 2 ceramics for LTCC with near zero temperature coefficient of resonant frequency

The Mg 3(VO 4) 2– xBa 3(VO 4) 2 ceramics have been investigated to obtain a low-temperature co-fired ceramic (LTCC). The highest quality factor ( Q f) of approximately 114,000 GHz was obtained when the ceramic with x = 0.2 was sintered at 950 °C for 5 h in air. The temperature coefficient of resonant frequency ( τ f) of the ceramics sintered at 1025 °C varied from −90 to 60 ppm/°C as the amount of xBa 3(VO 4) 2 increased, and was a near zero value in the sample obtained at x = 0.5 where the dielectric constant ( ɛ r) and the Q f values were approximately 12 and 55,000 GHz, respectively. In order to reduce the sintering temperatures of Mg 3(VO 4) 2– xBa 3(VO 4) 2 ceramics, the effects of Li 2CO 3 addition as a sintering aid on the microwave dielectric properties of Mg 3(VO 4) 2–0.5Ba 3(VO 4) 2 ceramics were also characterized in this study. The Li 2CO 3 addition was effective in reducing the sintering temperature without detrimental effects on the Q f values of the ceramics. One result: the microwave dielectric properties of Mg 3(VO 4) 2–0.5Ba 3(VO 4) 2 with 0.0625 wt%-doped Li 2CO 3 ceramic, which was sintered at 950 °C for 5 h in air, has a ɛ r value of 13, a Q f value of 74,000 GHz, and a τ f value of −6 ppm/°C.

Sintering temperature dependence of microwave dielectric properties in Mg 4(TaNb 1− xV x)O 9 compounds

The relationship between the sintering temperature and the microwave dielectric properties of Mg 4(TaNb 1− x V x )O 9 (MTNV) compounds were investigated in this study in order to reduce the sintering temperature of the compound. A small amount of V 2O 5 doping lowered the sintering temperature of the MTNV compounds. The variations in the dielectric constant and the quality factor of the MTNV compounds depended on the amount of V 2O 5 doping and the sintering temperature; a small amount of V 2O 5 doping was effective in allowing low sintering temperatures without a detrimental effect on these dielectric properties. As a result, a dielectric constant of approximately 12 and a quality factor of approximately 200,000 GHz were obtained when the MTNV compounds with x = 0.2 was sintered at 1200 °C. The temperature coefficient of resonant frequency of the MTNV compound with x = 0.025 slightly changed from −63 to −73 ppm/ °C with an increased sintering temperature because of the presence of a secondary phase.

Microwave dielectric properties of MgTiO 3–SrTiO 3 layered ceramics

MgTiO 3–SrTiO 3 layered ceramics with different stacking were fabricated and the microwave dielectric properties were evaluated with TE 011 mode. With increasing SrTiO 3 thickness fraction, the resonant frequency ( f 0) decreased, while the effective dielectric constant ( ɛ r,eff ) and temperature coefficient of resonant frequency ( τ f ) increased for the bi-layer ceramics. The stacking arrangement also had significant effect on the microwave dielectric properties. For the same SrTiO 3 thickness fraction of 0.333, the tri-layer MgTiO 3/SrTiO 3/MgTiO 3 ceramics had lower f 0, higher ɛ r,eff and τ f . The result was not consistent with the previous report on the layered ceramics with TE 011 mode [Cho, J. Y., Yoon, K. H. and Kim, E. S., Effect of stress on microwave dielectric properties of layered Mg 0.93Ca 0.07TiO 3–(Ca 0.3Li 0.14Sm 0.42)TiO 3 ceramics. Mater. Chem. Phys. 2003, 79, 286; Cho, J. Y., Yoon, K. H. and Kim, E. S., Correlation between arrangement of dielectric layers and microwave dielectric properties of Mg 0.93Ca 0.07TiO 3–(Ca 0.3Li 0.14Sm 0.42)TiO 3 ceramics. J. Am. Ceram. Soc. 2003, 86, 1330], where the effective dielectric constant was only determined by the thickness fraction and was independent of the stacking arrangement. Finite element analysis gave an explanation for the different microwave dielectric behaviors of the bi- and tri-layer ceramics in the present experiment.

Evaluation of electronic state of Mg 4(Nb 2− xSb x)O 9 microwave dielectric ceramics by first principle calculation method

The microwave dielectric properties of Mg 4(Nb 2− x Sb x )O 9 (MNS) solid solutions were evaluated and the variations in the electric state of the solid solutions were also investigated by using the first principle calculation method. The formation of a single phase was observed from the X-ray powder diffraction patterns of the solid solutions sintered at 1400 °C in the composition x from 0 to 1. The MgO and Mg 7Sb 2O 12 compounds were detected as the secondary phases at the compositions higher than x = 1; therefore, this result is closely related to the vaporization of Sb in this composition range. When comparing the overlap population of the (NbMg 12O 45) −61 cluster model with that of the (SbMg 12O 45) −61 cluster model, the slight covalency of the Sb O bond was recognized from the results of the first principle calculation method. In the composition range of 0–1, the Q· f values of MNS sintered at 1400 °C increased from 196,000 to 280,000 GHz; the dielectric constants of the solid solutions ranged from 13 to 10. However, an improvement in the temperature coefficient of resonant frequency with the Sb substitution for Nb was not recognized.

Low‐Temperature Synthesis and Microwave Dielectric Properties of Mg4Nb2O9 Ceramics Synthesized by a Precipitation Method.

AbstractFor Abstract see ChemInform Abstract in Full Text.