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This study established the connection between structure and dielectric responses by synergistically evaluating the chemical bond characteristics and lattice vibrational spectroscopies of trirutile ATa 2 O 6 (A = Mg, Ni) microwave ceramics. The MgTa 2 O 6 ceramic exhibits a uniform grain size distribution and a dense microstructure, with dielectric characteristics at microwave range of a ε r value of 27.27, a high Q × f value of 109,203 GHz (8.73 GHz), and a τ f of approximately 53.38 ppm/°C when sintered at 1300 °C, while the NiTa 2 O 6 ceramic presents a smaller average grain size and minor micropores, with dielectric characteristics at microwave range of ε r = 24.58, Q × f = 27,610 GHz (9.25 GHz), and τ f = 33.94 ppm/°C, sintered at 1250 °C. The structural refinement and atomic arrangements confirm a trirutile structure along the [001], [100], and [3 3 ‾ 1 ‾ ] zone axes. Ta–O bonds are found to contribute the most to the ionic character of a bond, bond susceptibility, lattice stability, thermal expansion behaviors, and strength of bonding ability, indicating their significant influence on dielectric polarization, lattice stability, and temperature coefficient of resonant frequency. Raman scattering spectra analysis reveals that the A 1g mode near 700 cm−1 mainly controls the Raman vibrational behaviors. The theoretical dielectric properties calculated from the infrared spectrum and dielectric properties analysis consistent with the measured dielectric performances, suggesting that the dielectric characteristics at the microwave range are mainly determined by the oscillatory absorption of structural phonons, with the first two modes at 210.48 cm−1 and 232.87 cm−1 contributing 72.02% to the ε r value and 90.45% to the tan δ value, respectively. [ABSTRACT FROM AUTHOR]

The Al 2 Mo 3 O 12 ceramic with monoclinic type is prepared at the sintering temperature as low as 750 °C, which exhibits excellent microwave dielectric properties of ε r = 4.99, Q × f = 49,579 GHz (f = 14.8 GHz), and τ f = −26 ppm/°C. The relationship between structure and characteristics is analyzed through the P–V–L chemical bond theory in depth, and the dielectric properties are investigated in combination with far-infrared spectroscopy. Results show that it is Mo–O bond that is responsible mainly for bond ionicity and dielectric polarizability, and structural stability as well. Based on the far-infrared reflectivity spectra and complicated dielectric function analysis, the calculated and measured results are in relative agreement using the classical damped oscillation mode, indicating that the mode at 80.23 cm−1 is dominant for the contribution to dielectric properties. This study gives an insight into the structural characteristic and provides a guide to further improve the microwave dielectric performance of Al 2 Mo 3 O 12 ceramic. [ABSTRACT FROM AUTHOR]

This study prepared glass doped 0.95MgTiO 3 –0.05CaTiO 3 (95MCT) ceramics with excellent microwave dielectric properties via phase constituent regulation. Based on XRD and semi-quantitative analysis, it is found that the types of glass, addition amounts of glass, and sintering method can introduce different phase compositions. With the aid of the low softening point for glass materials and the liquid phase sintering mechanism, the 95MCT ceramics can be densified at a relatively low temperature. Meanwhile, based on the mixture rule, adjusting the proportion of each phase structure by altering the sintering method, the optimum temperature (1200 °C) for 95MCT ceramics is reduced by about 200 °C without deteriorating performance. Typically, the 95MCT ceramic doped with 1 wt % ZnO–B 2 O 3 –SiO 2 glass demonstrates excellent microwave dielectric properties: ε r = 18.3, Q × f = 50824 GHz (@7.9 GHz). [ABSTRACT FROM AUTHOR]

This work studied the phase constitution, bond characteristics, and microwave dielectric performances of Sr2TiO4 ceramics. Based on XRD and Rietveld refinement analysis, pure tetragonal Ruddlesden–Popper type Sr2TiO4 ceramic is synthesized at 1425~1525 °C. Meanwhile, the microstructure is dense and without porosity, indicating its high sinterability and densification. Great microwave dielectric performances can be obtained, namely an εr value of 39.41, and a Q × f value of 93,120 GHz, when sintered at 1475 °C. Under ideal sintering conditions, the extrinsic factors are minimized and can be ignored. Thus, the intrinsic factors are considered crucial in determining microwave dielectric performances. Based on the P–V–L complex chemical bond theory calculation, the largest bond ionicity, and proportions to the bond susceptibility from Sr–O bonds suggest that Sr–O bonds mainly determine the dielectric polarizability. However, the Ti–O bonds show lattice energy about three times larger than Sr–O bonds, emphasizing that the structural stability of Sr2TiO4 ceramics is dominated by Ti–O bonds, and the Ti–O bonds are vital in determining the intrinsic dielectric loss. The thermal expansion coefficient value of the Sr2TiO4 structure is also mainly decided by Ti–O bonds. [ABSTRACT FROM AUTHOR]

As one of the main crystalline phases of A6 tape (Ferro Corp.), CaSiO3 is a promising candidate with excellent microwave dielectric traits, including a low dielectric constant and a low dielectric loss. The optimum sintering temperature of CaSiO3 ceramic can be reduced from 1250 to 925 °C with a high Q×f value after adding LiF additive. Therefore, the phase constitutions, microstructure, low-temperature sintering behaviors, and microwave dielectric traits of CaSiO3 ceramics doped with 0.5 ~ 3 wt% LiF were investigated in detail. In particular, the outstanding microwave dielectric traits (εr = 6.3, Q×f = 32,435 GHz, τf = − 28.51 ppm/°C) achieved in the CaSiO3 ceramics with 1 wt% LiF are compatible with silver when sintering at 875 °C, showing great potential for the application of low-temperature co-fired ceramic (LTCC) technology. [ABSTRACT FROM AUTHOR]

In this article, the strategy of co-doping Mn2+ ions with W6+ ions is used to improve the comprehensive dielectric performances of TiO2 ceramics. According to the analysis of XRD results, a pure TiO2 phase with a rutile structure can be found throughout the whole substitution range (0 ≤ x ≤ 0.02). Based on the refinement method, it is noted that the tetragonality firstly increase for 0 ≤ x ≤ 0.005, and then decreases for x > 0.005. A slight blue shift is observed for the A1g mode, whereas the Eg mode shows a red shift. The permittivity is highly dependent on the relative density, fc of Ti/(Mn0.5W0.5)-O1(1) and Ti/(Mn0.5W0.5)-O1(2) bond and Afc. The variation of quality factor strongly relies on the relative density, changing c/a value and valence state of Ti. The increase of c/a and elimination of Ti3+ contribute to the significant improvement of Q × f from 947 to 39,000 GHz. The τf dramatically decreases from 520 to 398 ppm/ºC because of the increase of unit cell volume. The excellent dielectric performance of Ti1-x(Mn0.5W0.5)xO2 ceramics can be achieved at x = 0.005 with εr = 105, Q × f = 39,000 GHz and τf = 464.4 ppm/ºC. [ABSTRACT FROM AUTHOR]

In this study, (Ti1/2W1/2)5+ ionic co-substitution effects on the crystal structural evolution, microstructure, and microwave dielectric characteristics of wolframite MgZrNb2O8 ceramics were studied in detail. From the Rietveld refinement analysis, the (Ti1/2W1/2)5+ cation diffuses into the Nb site and forms a solid solution; meanwhile, the increasing content of (Ti1/2W1/2)5+ cation from x = 0.02 to x = 0.08 decreases the volume cell, resulting in the shrinkage of the unit cell. The microstructures of ionic doped MgZrNb2O8 ceramics are compact; however, the sintering temperature benefits the growth of grain and the densification, where the highest density is achieved at x = 0.06. For the development of the microwave dielectric properties, the relative permittivity (εr) gradually declines as x increases, which is mainly ascribed to the small dielectric polarizabilities of (Ti1/2W1/2)5+ cation; however, the Q × f value is internally affected by the packing fraction and the size uniformity of grain distribution. The distortion of [NbO6] octahedral is mainly responsible for the variation of the τf value. [ABSTRACT FROM AUTHOR]

In the present study, ionic substitution strategies were adopted in ixiolite Zn 0·5 Ti 0·5 NbO 4 ceramics, where the Co2+ and Ta5+ cations were used to partially replace the Zn and Nb sites and to investigate the structural evolution and microwave dielectric performances. It is interesting to find that the substitution of Co2+ and Ta5+ cations both lead to the reduction of volume of the unit cell, however, the variations of chemical bond behaviors are different, which is explained by the Rietveld refinement method, normalized bond analysis, polyhedral stretching behaviors, and the changes of characteristic Raman peaks. Furthermore, based on the complex chemical bond theory calculation, the drop of dielectric constant within the solid solution limits is attributed to the decline of average bond ionicity value along with the increase of ionic substitution content; while the lattice stability and uniformity of grain growth are mainly responsible for the variations of Q f value. After exceeding the solid solution limits, the developments of dielectric performances of Zn 0·5 Ti 0·5 NbO 4 ceramics are more sensitive to the regulation of the secondary rutile phase. More importantly, the intrinsic dielectric properties analysis indicates that the absorption of structural phonon oscillation mainly causes the dielectric response in the microwave range. [ABSTRACT FROM AUTHOR]

In the present study, combined usage of cobalt and tantalum ionic substitution strategy was adopted on the (Zn1−xCox)0.5Ti0.5(Nb0.9Ta0.1)O4 ceramics, where the phase constitutions and microwave dielectric properties were investigated. It is shown that a finite ixiolite-type Zn0.5Ti0.5NbO4 solid solution can only be synthesized at x = 0–0.1. With the increase of cobalt ionic content at x = 0.2–0.3, a formation of a rutile phase indexed as Zn0.15Nb0.3Ti0.55O2 was detected, which is testified by the Rietveld refinement method and Raman spectra analysis. Benefitted by the appearance of the secondary phase, the microwave dielectric properties, especially the τf value of (Zn1−xCox)0.5Ti0.5(Nb0.9Ta0.1)O4 ceramics were greatly improved, which well agrees with the theoretical prediction of dielectric properties based on mixture rule. Based on the results, it indicates that an excellent promotion effect of the combined usage of cobalt and tantalum oxides can benefit the microwave dielectric properties of the Zn0.5Ti0.5NbO4-based ceramics. Specifically, the (Zn1−xCox)0.5Ti0.5(Nb0.9Ta0.1)O4 (y = 0.1, x = 0.25) ceramic synthesized at 1175 °C shows excellent microwave dielectric properties: εr = 40.3, Q × f = 22,054 GHz,, and τf = − 5.2 ppm/oC. [ABSTRACT FROM AUTHOR]

In this study, BaSi 2 O 5 ceramics with an orthorhombic structure were synthesized by using a traditional solid-state method at a low temperature by doping with Li 2 O–B 2 O 3 –CaO–CuO (LBCC) glass. The phase composition, mechanism of low-temperature sintering, microwave dielectric properties, and changes in the mesophase during the heating of low-temperature sintered BaSi 2 O 5 ceramics were examined by performing an X-ray diffraction analysis. A compact matrix of BaSi 2 O 5 can be wetted by the liquid phase of the formed LBCC glass. Therefore, LBCC glass with different doping percentages can effectively reduce the sintering temperature of BaSi 2 O 5. The microwave dielectric properties of BaSi 2 O 5 ceramics sintered at 900 °C at 4 wt% of LBCC glass were determined: ε r = 7.32, Q × f = 19,002 GHz, and τ f = −35.8 ppm/°C. The chemical compatibility of the samples with Ag was studied at 4 wt% doping with LBCC glass, and the samples were fired for 4 h at 900 °C. [ABSTRACT FROM AUTHOR]

In this study, single-phase MgZr1−x(Mg1/3Ta2/3)xNb2O8 (0 ≤ x ≤ 0.08) ceramics with monoclinic wolframite structure were synthesized by the traditional solid-state method. The influences of (Mg1/3Ta2/3)4+ substitution for Zr4+ on phase composition, microstructure, packing fractions, bond valences, and the microwave dielectric properties of the ceramics were systematically investigated. According to the Rietveld refinement results, with the doping of (Mg1/3Ta2/3)4+, the decline of unit cell volume led to the shift of the main peak in XRD pattern to a higher angle. Furthermore, the trend of the experimental dielectric constant kept in line with the theoretical dielectric constant calculated by the Shannon complex polarizability theory. With the introduction of (Mg1/3Ta2/3)4+ ion, the Q × f values were greatly improved due to the increase of the packing fractions, but the porosity caused by excessive substitution deteriorates the quality factor. The increase of B-site bond valence explained the decline of τf. In particular, the MgZr1−x(Mg1/3Ta2/3)xNb2O8 (x = 0.04) ceramics sintered at 1340 °C for 4 h exhibited optimal microwave dielectric properties of εr = 25.42, Q × f = 65,950 GHz, and τf = − 61.04 ppm/°C. [ABSTRACT FROM AUTHOR]

In the present research, structural representation, phase transition, and dielectric characteristics of Ta5+ ionic substituted Co 0.5 Ti 0.5 (Nb 1- x Ta x)O 4 (x = 0–1) ceramics were thoroughly investigated. Combined with the changes of diffraction peaks in the X-ray diffraction spectra, such as (002) and (101) crystalline planes near 20°, and the evolutionary trend of the strongest peak in the Raman spectra, a phase transition from rutile to trirutile structure at x = 0.6 was confirmed, suggesting the emergence of structural evolution. Thus, the structural evolution showed a significant impact on the dielectric characteristics, as evidenced by the weakening of the dielectric polarizability with the increasing amount of Ta5+ ion, which led to a reduction in the dielectric constant; the dielectric loss is also closely related to the packing fraction (PF) arising from the structural changes. Additionally, infrared and THz time-domain spectroscopy revealed that the dielectric losses in the microwave band were originated from the oscillatory absorption of structural phonons and supported that the effects of structural evolution on the intrinsic dielectric properties due to the introduction of Ta5+ ion. [ABSTRACT FROM AUTHOR]

In this article, the (Mn 1/2 W 1/2)4+ complex cation co-doped ilmenite MgTiO 3 ceramics with improved microwave characteristics were synthesized. The correlations between the crystal structural evolution induced by ionic substitution and the microwave characteristics were investigated using the structural analysis and the P–V–L bond theory. Theoretically, the Mg–O bond should have a larger value of covalency than Ti–O bond, attributing to the distribution of densities of states, where the s and p states of the Mg atom overlap with those of the O atom. This conclusion fits well the bond theory estimation. The dielectric constant is dominated predominantly by the average bond covalency, which is intrinsically caused by the increase of doping contents. Moreover, the structural stability declines slightly with the increase of (Mn 1/2 W 1/2) contents. From the perspective of structural evolution, this dielectric performance is also reflected by the variations of the Raman shift and the FWHM value of A g 5 mode. The actual Q × f value, however, experiences a great enhancement at x = 0.010, which benefits generally from the uniformity of the grain size and the inhibition of reduction of Ti4+ valence. The excellent microwave characteristics of MgTi 0.99 (Mn 1/2 W 1/2) 0.01 O 3 ceramics were achieved: a ε r of 18.74, a Q × f value of 160992 GHz and a τ f of −58.2 ppm/°C, when sintered at 1325 °C. [ABSTRACT FROM AUTHOR]

Gd2Zr3(MoO4)9 is a double trigonal molybdate crystallized in the space group R3¯c. The optimal microwave dielectric properties were achieved via solid‐state reaction at 725°C for Gd2Zr3(MoO4)9 ceramics: εr = 11.17, Q × f = 57 460 GHz, τf = −31.91 ppm/°C. The three‐dimensional framework type structure is formed by mixed MoO4 tetrahedron and ZrO6/GdO9 polyhedron. The analysis based on complex chemical bond theory shows that the Mo–O bonds account for majority contribution to controlling microwave dielectric properties. The MoO4 tetrahedron and ZrO6 octahedron stabilize the crystal structure by strong binding ability. As it was shown by Raman spectroscopy, the Raman‐active vibrations primarily originate from MoO4 tetrahedron, similarly to molybdate analogies. [ABSTRACT FROM AUTHOR]

Structure‐property relationships of Y2MgTiO6, a type of double perovskite materials, were investigated systematically. Rietveld refinement of XRD patterns confirmed that Y2MgTiO6 belongs to the P21/c space group and has a structure analogous to that of monoclinic Dy2MgTiO6. In accordance with the observed number of vibrational bands and group theoretical predictions, O and Y ions at the 4e site dominated the Raman peaks. The IR reflectivity spectrum indicated that the major contributions to the relative permittivity and intrinsic loss were modes lower than 500 cm−1. The measured relative permittivity closely approached the calculated values determined according to P‐V‐L theory, the Clausius‐Mossotti equation and IR fitted results. The larger bond energy for Mg–O bonds than for Ti–O bonds corresponds to a more stable octahedron of [MgO6], as verified by the octahedral distortion. Satisfactory microwave dielectric properties of Y2MgTiO6 ceramics were as follows: εr = 20.4 ± 0.8, Q × f = 42 060 ± 310 GHz, τf = −52 ± 3 ppm/°C, sintered at 1450°C. [ABSTRACT FROM AUTHOR]

In this study, the crystal structure, phase composition, Raman spectrum, and microwave dielectric properties of novel Co 0.5 Zr 0.5 TaO 4 ceramics were investigated. Based on the X-ray diffraction, Rietveld refinement analysis and Raman spectroscopy, a coexistence of monoclinic-type and trirutile tetragonal phases was confirmed in the temperature range of 1100–1200 °C. The variations of relative density, growth of grain, and contents of each phase are mainly responsible for the developments of microwave dielectric properties of Co 0.5 Zr 0.5 TaO 4 ceramics. Excellent microwave dielectric properties with a ε r of 20.19, a Q × f about 65125 GHz and a τ f ca. of −39.02 ppm/oC were obtained when sintered at 1150 °C. [ABSTRACT FROM AUTHOR]

The influences of Zr4+ substituted for Ti4+ on the microwave dielectric properties of LiNb0.6Ti(0.5−x)ZrxO3 (0.00 ≤ x ≤ 0.14) ceramics prepared via conventional solid-state method have been studied and are discussed. X-ray diffraction analysis indicated that the Li1.075Nb0.625Ti0.45O3 phase was formed, while a small trace of ZrO2 was observed when x reaches 0.08. With the increase of Zr4+ substitution, variation of the dielectric constant (εr) was dominated by phase constitutions and densification. The quality factor (Q × f) showed a continuously decrease tendency, which was attributed to the increasing number of grain boundaries and the content of the secondary phase. The temperature coefficient of the resonant frequency (τf) value shifted from 30.60 ppm/°C to − 14.50 ppm/°C. Temperature-stable microwave dielectric ceramics was obtained with εr = 63.14, Q × f = 4626 GHz and τf =1.38 ppm/°C, at x = 0.10. [ABSTRACT FROM AUTHOR]

Abstract In this study, the influence of substitution of Zr for Ti on crystal structure and microwave dielectric properties of Zn 0.15 Nb 0.3 (Ti 1- x Zr x) 0.55 O 2 (0 ≤ x ≤ 0.7) ceramics were discussed through Rietveld refinement, normalized bond analysis and complex chemical bond theory. Rietveld refinement analysis indicated that a composite could be formed for x ≤ 0.22. Pure orthorhombic type (O-type) solid solutions are prepared in the region of x = 0.3–0.7. With the increasing amount of ZrO 2 , cell volume of O-type phase increases, and it results in the enlarging and compressing behaviors of chemical bonds. Under the circumstances, the dielectric polarizability is deteriorated because of the reducing chemical bond covalency value (f c), and this finding is also confirmed by Clausius-Mosotti equation. Lattice energy of Zr–O1 bonds and grain size distribution of sintered specimens are mainly responsible for the variations of quality factor (Q × f) value. Chemical bond energy (E) is closely related with the temperature coefficient of resonant frequency value (τ f). Typical microwave dielectric properties of Zn 0.15 Nb 0.3 (Ti 1- x Zr x) 0.55 O 2 ceramics (x = 0.22) were obtained when sintered at 1100 °C: ε r = 46.31, Q × f = 30,297 GHz, τ f = -8.24 ppm/°C. [ABSTRACT FROM AUTHOR]

In this work, (1 − x)Mg2Al4Si5O18-xMg2SiO4 (x = 0-80 wt%) composite dielectric ceramics were prepared via traditional solid-state reaction. The results indicate the sinterability of Mg2Al4Si5O18 ceramics is greatly enhanced with the increasing content of Mg2SiO4 by reducing densified temperature from 1460 to 1340 °C. Rietveld refinement analysis shows a great chemical compatibility between two phases. With the increase of Mg2SiO4 content, the densifications of ceramics can be improved. However, excessive amount of Mg2SiO4 induces abnormal grain growth, which deteriorates the microwave dielectric properties. At x = 50 wt%, low-εr dielectric ceramics with high Q × f value was obtained when sintered at 1340 °C: εr = 5.73, Q × f = 76,374 GHz and τf = − 24 ppm/ °C. Relative cheap raw materials and adjustable permittivity values, which makes it promising for low-permittivity microwave applications. [ABSTRACT FROM AUTHOR]

Abstract: Single phase of dense ixiolite structure Zn0.5Ti0.5NbO4 (ZTN) microwave dielectric ceramics were synthesized at low temperature (850°C‐900°C) via solid state reaction with small amount of Li2O‐B2O3‐SiO2 (LBS) glass. There is a liquid phase generated by LBS at about 760°C, which significantly enhances the shrinkage and decreases the activation energy. And with the assistance of liquid phase, single phase of ZTN with orthorhombic structure is detected, sintering temperature of ceramics drops from 1125°C to 850°C and still maintain high relative density (>97%) with great microwave dielectric properties (εr ~ 34.32, Q×f ~ 17740 GHz). Ceramics with 0.5 wt. % LBS cannot be sintered and densified, and the lack of densification determines a lower dielectric constant, large dielectric loss, and undetectability of temperature coefficient of resonant frequency. With the increase in LBS, a dense structure can be formed, but the deterioration of performance should be mainly attributed to the variation in LBS glass content. [ABSTRACT FROM AUTHOR]

The lithium silicate glass-ceramic was synthesized by conventional solid-state methods at low sintering temperatures. The effects of different sintering temperature on the crystal composition, microstructure, flexural strength, bulk density, thermal expansion coefficient (TEC) and microwave dielectric properties of lithium silicate glass ceramic have been investigated in detail. The research shows that the lithium silicate ceramic was synthesized successfully at a lower temperature (1010 °C). Excellent properties obtained at 1010 °C for 30 min: the flexural strength σ = 189.782 Mpa, the coefficient of thermal conductivity λ= 7.807 w/(m k), ε = 6.11, Q × f = 3686 GHz, the bulk density was 2.429 g/cm and α = 10.6992 × 10/°C, indicating its potential value for LTCC application. [ABSTRACT FROM AUTHOR]

Conventional solid-state methods were used to synthesize MgSiO ceramic at relatively low sintering temperatures with the assistance of CaO-BO-SiO (CBS) glass. The effects of the CBS additions on the sintering behavior, crystal structures, microstructures, and microwave dielectric properties of MgSiO ceramic have been investigated in detail. The results indicate that the addition of CBS glass lowered the sintering temperature of MgSiO ceramic significantly. The MgSiO ceramic with 7 wt.% CBS addition sintered at 1325°C for 4 h shows excellent microwave dielectric properties: ε = 6.47, Q × f = 16,552 GHz, τ = −23.34 ppm/°C. [ABSTRACT FROM AUTHOR]

• Temperature stable Co 0.5 Sn 0.5 TaO 4 ceramic was synthesized using solid state method. • Structural-property relationship was established. • Dielectric properties at microwave and THz range were investigated. • ε r = 18.6, Q × f = 36875 GHz (10.3 GHz), TCF = −0.6 ppm/°C, and tanδ = 8.3 × 10−3 (0.6 THz) were achieved. Co 0.5 Sn 0.5 TaO 4 ceramic was fabricated in this study, where the structural configuration and dielectric properties were discussed. A trirutile-type was confirmed via X-ray diffraction, Raman scatting spectroscopy, and TEM analysis. Temperature-stable Co 0.5 Sn 0.5 TaO 4 ceramic with excellent microwave dielectric properties of an ε r value ∼18.6, a Q × f value about 36875 GHz (10.3 GHz) was achieved under TE 011 mode; moreover, a tanδ value as low as ∼8 × 10−3 was also identified at 0.6 THz, showing prospects in high-frequency applications. [ABSTRACT FROM AUTHOR]

In this study, (Cu 1/3 Nb 2/3)4+ complex cation and BaO–ZnO–B 2 O 3 glass frit were adopted to solve the high sintering temperature and poor temperature stability of Ba 3 Nb 4 Ti 4 O 21 ceramics. It is shown that pure Ba 3 Nb 4 Ti 4 O 21 phase was formed when Ti site was partially replaced by (Cu 1/3 Nb 2/3)4+ cation. The increasing number of dopants decreases the dielectric polarizability, correspondingly, the dielectric constant and temperature coefficient of the resonance frequency values are reduced consistently. The variation of the Q × f value is determined by internal ionic packing fraction and external sintering densification. The (Cu 1/3 Nb 2/3)4+ cation effectively decreases the suitable sintering temperature from 1200 to 1050 °C while greatly improving the temperature stability. BaO–ZnO–B 2 O 3 glass was used to further improve the low-temperature sintering characteristics of Ba 3 Nb 4 Ti 4 O 21 ceramics. It is proven that the addition of glass frits effectively decreases the temperature to 925 °C with combinational excellent microwave dielectric properties: ε r ∼55.6, Q × f ∼5700 GHz, τ f ∼3 ppm/°C, making the Ba 3 Nb 4 Ti 4 O 21 ceramics promising in the applications of low-temperature cofired ceramic technology. [ABSTRACT FROM AUTHOR]

Coordination chemistry, bond state and vibrational spectrum of co-substituted microwave dielectric NdNb 1- x (Zr 0.5 W 0.5) x O 4 ceramics (x = 0.01∼0.05) were investigated. Raman spectra and XRD refinement showed a solid solution was formed. The compressed and elongated chemical bonds are responsible for the variations of crystal parameters and cell volume. Calculated chemical bond parameters indicated bond covalency, lattice energy and Nb-site bond energy act on the fluctuations of the permittivity, quality factor and temperature coefficient, respectively. Meanwhile, the infrared vibrational spectrum is fitted to quantify the contributions of observed IR mode to the intrinsic loss. Compact ceramic possesses excellent properties: ε r ∼ 19.2, Q × f ∼ 55282 GHz and τ f ∼ -11.36 ppm/°C with x = 0.04, at 1250°C. [ABSTRACT FROM AUTHOR]

A novel microwave dielectric ceramic LiNb 0.6 Ti 0.5 O 3 (LNT) with Ca substitutions LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 was synthesized by solid-state method. It was found that with Ca substitutions, the temperature coefficient of resonant frequency τ ƒ could be adjusted to zero, due to the appearance of the second phase Ca 5 Nb 4 Ti 3 O 21 . The τ ƒ of the Ca 5 Nb 4 Ti 3 O 21 phase is −144.3 ppm/°C through the simulation and numerical value calculation. Furthermore, the LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 ceramic shows a higher dielectric constant ε r and a denser microstructure. The LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 ceramic with x = 0.03 sintered at 1100 °C for 2 h shows excellent microwave dielectric properties: ε r = 76.89, Q × ƒ = 4064 GHz, τ ƒ = 0.25 ppm/°C. [ABSTRACT FROM AUTHOR]

New types of multi-component Li 3+ x Mg 2–2 x Nb 1- x Ti 2 x O 6 (0 ≤ x ≤ 1) solid-solution ceramics were designed based on the Li 2 TiO 3 −Li 3 NbO 4 −MgO pseudo ternary phase diagram and studied for microwave dielectric applications. As the substitution amount (x) increased, we detected the phase transitions among the orthorhombic, cubic, and monoclinic phase driven by the compositional changes, as well as accompanied by an order-disorder-order transformation. A full range of solid solutions was formed between the Li 3 Mg 2 NbO 6 and Li 2 TiO 3 endmembers, with no trace of other impurities. In the sample with the low substitution concentration (x = 0.2 mol), a coherent phase interface (CPI) between the cubic and orthorhombic lattices was formed with no obvious misfit dislocation or stacking fault, indicating the small differences in crystal configuration, chemical bonding properties, and subcell lattice parameters between the two phases. Besides, there were observed diverse reconstructed superlattices, one kind is that possessed a "transition form" of the two phases and was formed nearby the CPI, and the other kind was formed based on the cubic or orthorhombic lattices independently and was observed on a larger scale nearby the CPI. The preferential substitutions of the non-equivalent cations, which were determined by ionic radius, electronegativity, and local electroneutrality, and the interfacial strains would together act on the formation of these superlattices. The Q × f values measured in the microwave range increased considerably around the compositional range where the superlattices were formed, indicating that the effect of reconstructed superlattices on the intrinsic loss should not be overlooked. As proven by the dielectric response in the high-frequency range (0.5 − 1 THz), the x = 0.2 sample indeed showed extremely higher Q × f values than other ones, which illustrated that the sample with the reconstructed superlattices was related to a small lattice vibrational anharmonicity that is favorable for the low dielectric loss. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A novel low-loss and temperature stable NiSnTa 2 O 8 ceramic with trirutile structure was prepared using traditional solid-state method. The structure-performance relationships were investigated by Rietveld refinement, chemical bond theory and far-infrared spectrum. The results show that the relative densities play a dominant role in the change of dielectric constant. Theoretical dielectric constant calculated via bond theory, Clausius-Mossotti equation and fitted result of far-infrared spectrum are close to experimental value. Ta–O bonds with greatest bond ionicity and bond energy have the primary contributions to dielectric polarizabilities and dielectric loss. The optimal microwave dielectric performances of NiSnTa 2 O 8 ceramics were obtained: ε r ∼21.04, Q×f ∼31328 GHz and τ f = −2.63 ppm/°C at 1425 °C. [ABSTRACT FROM AUTHOR]

Mg 2 (Ti 1- x Sn x)O 4 (x = 0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg 2 (Ti 1- x Sn x)O 4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg 2 (Ti 1- x Sn x)O 4 compounds were obtained ( ε r = 12.18, Q × f = 170,130 GHz, τ f = −53.1 ppm/°C, x = 0.2). [ABSTRACT FROM AUTHOR]

Abstract The phase composition, microstructure, microwave dielectric properties of (Al 0.5 Nb 0.5)4+ co-substitution for Ti site in LiNb 0.6 Ti 0.5 O 3 ceramics and the low temperature sintering behaviors of Li 2 O-B 2 O 3 -SiO 2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li 1.075 Nb 0.625 Ti 0.45 O 3 solid solution was formed in all component. The increase of dielectric constant (ε r) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τ f value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb 0.6 Ti (0.5- x) (Al 0.5 Nb 0.5) x O 3 ceramics (x = 0.10) when sintered at 1100 ℃ for 2 h: ε r = 70.34, Q×f = 5144 GHz, τ f = 4.8 ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x = 0.10 were obtained with 1.0 wt% glass: ε r = 70.16, Q×f = 4153 GHz (at 4 GHz), τ f = -0.65 ppm/℃ when sintered at 925 ℃ for 2 h. [ABSTRACT FROM AUTHOR]

We studied the phase constitutions, microstructure, chemical bond and microwave dielectric properties for Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 (0 ≤ x ≤ 0.03) ceramics synthesized by solid-state reaction using SEM, X-ray diffractometer, Raman spectroscopy, microwave measuring system, etc. Although the second phase TiO 2 appeared when x ≥ 0.015 as presented in XRD patterns, TiO 2 was confirmed to have no effects on the tendency of microwave dielectric properties as a function of x value. The SEM images showed that the grain size decreased as Cr content increased, which could be explained by that doping Cr increased the grain boundary energy or decreased surface energy for Ca 0.61 Nd 0.26 TiO 3 ceramic. The SRO effects enhanced with increase of Cr substitution, which was verified by Raman spectra. The dielectric constant and τ f value were concerned with the average ionicity of chemical bond and the ionic polarizability for Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 ceramics. The SEM images suggested that the optimized sintering temperatures was 1400 °C for samples with x = 0.01. The XPS spectra and the trend of Q × f value indicated that the balanced amount of Cr substitution could restrain the generation of Ti3+. Hence, the Q × f value of Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 ceramics reached the maximum of 16,078 GHz at x = 0.01 compared with that of 11,425 GHz in pure Ca 0.61 Nd 0.26 TiO 3 ceramic. • The Ca 0.61 Nd 0.26 Ti 0.99 Cr 0. 0 1 O 3 ceramic had maximum Q × f value of 16,078 GHz. • The SRO effect enhanced with increase of Cr3+. • The balanced amount of Cr substitution could restrain the generation of Ti3+. [ABSTRACT FROM AUTHOR]