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The Ba(VO)-x wt% CoO (x = 0.5-5) ceramics were prepared by the solid state reaction method in order to reduce the sintering temperature. The effects of the CoO additions on the phase composition, microstructures, sintering characteristics and microwave dielectric properties of Ba(VO) ceramics are investigated by an X-ray diffractometer, a scanning electron microscope and a network analyzer. As a result, the Q × f value of 54,000 GH, the ε of 14.6 and the τ value of +58.5 ppm/°C were obtained in the sample of the Ba(VO)-3 wt% CoO ceramic sintered at the temperature of 925 °C, which is capable to co-fire with electrode metal of high conductivity such as Ag (961 °C). Moreover, the Q × f values of the sample with CoO higher than that of 3 wt% additions decreased because of the formation of BaVO phase. [ABSTRACT FROM AUTHOR]

High sinterability nano-YO powders for transparent ceramics were successfully synthesized via the decomposition of hydroxyl-carbonate precursors from spray coprecipitation. The chemical composition of the precursor was determined as Y(CO)(OH)· nHO ( n = 1-1.5), and it was evolved into YO particles with clear facets after calcination with the assistance of sulfate. Two dispersion mechanisms, 'absorption' and 'intercalation,' were proposed to work together to provide the dispersion effect. Microstructural and optical characterization of powders and as-fabricated transparent ceramics was employed to evaluate the sintering behavior of powders. The nanopowders calcined at 1250 °C had weakly agglomerated morphology with the mean particle size of ~140 nm and exhibited excellent sinterability. The in-line transmittance of YO ceramic of 1 mm thickness that was vacuum sintered at 1800 °C for 8 h without any sintering additives reached 78.7% at 1064 nm. [ABSTRACT FROM AUTHOR]

BaZrTiO ceramics are prepared via the conventional solid state reaction method. The Zr ions have diffused into the BaTiO lattices to form a homogenous solid solution. We investigate the dielectric properties and energy storage density of BaZrTiO ceramics at different sintering temperature. The temperature dependence of dielectric constant of BaZrTiO ceramics illustrates the obvious relaxor phase transition characteristics. The polarization hysteresis loops P-E of ceramics sintered at 1260-1300 °C show slimmer comparable to that of ceramics sintered at 1240 °C, resulting in high energy storage density. Excellent dielectric properties and energy storage density are achieved in the BaZrTiO ceramics sintered at 1260 °C for 2 h: ε = 2998, tanδ = 0.007 and J = 0.5 J cm. [ABSTRACT FROM AUTHOR]

This paper reported the fabrication of YO transparent ceramics with γ-AlO doped as the sintering aid under vacuum using the co-precipitated YO powders as raw materials. The different concentrations of γ-AlO were employed for investigating the effect on the microstructures and densities of YO ceramics. The doped sintering aid could achieve fine microstructure and high density. The average grain sizes were around 25 μm, and the relative densities were all above 98.5 %. The best sample was achieved with 0.08 wt% γ-AlO when sintered at 1850 °C for 8 h. And the grain size and relative density were 25 μm and 99.47 %, respectively. [ABSTRACT FROM AUTHOR]

(ZrSn)TiO (ZST) ceramics were prepared by conventional solid-state ceramic method. The effects of ZnO + CeO on the phase composition, microstructure, sintering characteristics and microwave dielectric properties of ZST ceramics were investigated. Only a single phase (ZrSn)TiO was identified for XRD patterns. The sintering temperature decreased from 1550 to 1220 °C owning to the composite addition of ZnO and CeO. The excellent microwave dielectric properties have been obtained in the samples of ZnO (1 wt%) + CeO (0.5 wt%) doped ZST ceramics sintered at 1220 °C for 4 h: ε = 37, Q × f = 33,000 GHz, τ = −0.76 ppm/°C. [ABSTRACT FROM AUTHOR]

Microwave dielectric ceramics with the composition of Ba(CoNb)O-MnO (BCN-MnO) were prepared by the solid-state reaction method. The effects of MnO on phase composition, microstructure, sintering characteristics and microwave dielectric properties of BCN ceramics were investigated. The additive MnO slightly decreased the sintering temperature and improved the densification of BCN as sintering aids. The multivalent Mn was beneficial for maintaining the compositional stability of BCN, which broadened the region of the sintering temperature. The Q × f value and temperature coefficient of resonant frequency ( τ) were improved by 0.3 wt% MnO. BCN-0.3 wt% MnO ceramic sintered at 1,340 °C for 12 h in air exhibited good microwave dielectric properties with ε = 32.9, Q × f = 90,431 GHz, τ = −12 ppm/°C. [ABSTRACT FROM AUTHOR]

MnO doped BaNdTiO-NdAlO(13 wt%) (BNT-NA) microwave dielectric ceramics with the near zero τ and the wide range of sintering temperature were prepared by conventional solid state method. The effects of Mn doping on the microstructures and microwave dielectric properties of BNT-NA ceramics were investigated. XRD patterns showed only a single BaNdTiO phase was identified in all samples and there was no second phase. The sintering temperature decreased from 1,380 to 1,320 °C as MnO content increased from 0.1 to 0.9 wt%. The MnO doped BNT-NA ceramics could be densified at a lower sintering temperature. The MnO additive had a positive effect on lowing sintering temperature of BNT-NA ceramics. The τ varied from negative to positive with the increase of MnO. Excellent microwave dielectric properties were achieved in BaNdTiO-NdAlO ceramics doped with 0.3 wt% MnO and sintered at 1,380 °C for 2 h: ε = 66.5, Q × f = 13,948 GHz, τ = 0.4 ppm/°C. [ABSTRACT FROM AUTHOR]

High optical quality holmium doped yttrium aluminum garnet ( Ho:YAG) transparent ceramics that contained 0.5-2.0 at.% holmium additives were fabricated by a reactive sintering method under vacuum. Fully dense Ho:YAG ceramics with the average grain size of ~10 μm were obtained after vacuum sintered at 1780°C for 8 h. The in-line transmittances in the visible and infrared region are higher than 82% and 84%. The absorption coefficients of the 0.8, 1.0, 1.5, and 2.0 at.% Ho:YAG ceramics at 1907 nm was calculated to be 0.72, 0.89, 1.32, and 1.78 cm−1, respectively. The absorption cross-section of Ho:YAG ceramic was 0.645 × 10−20 cm2. The 1.5 and 2.0 at.% Ho:YAG ceramic slabs were in-band pumped by a Tm:fiber laser at 1907 nm. A maximum output power of 20.6 W at 2097 nm was obtained with a corresponding slope efficiency of 60.9%. [ABSTRACT FROM AUTHOR]

(1-x)Li 2 Mg 2 Mo 3 O 12 -xTiO 2 (x = 0.1–0.5) composite ceramics are prepared by solid-state sintering process. And the structure, composition, microwave dielectric properties and ultra-low temperature sintering characteristics are studied. The result of two-phase (Li 2 Mg 2 Mo 3 O 12 and TiO 2) coexistence is definitely identified through XRD, mapping and Raman analysis along different regions. Furthermore, as the sintering temperature increases, the enhanced degree of densification plays a positive role in determining microwave dielectric properties. Sintering additives are used to lower sintering temperature of 0.6Li 2 Mg 2 Mo 3 O 12 -0.4TiO 2 composite ceramics, where 1 wt% H 3 BO 3 is applied to reduce the temperature from 750 °C to 700 °C and maintain excellent microwave dielectric characteristics. The cooling mechanism of sintering aids are also thoroughly studied. In all, 0.6Li 2 Mg 2 Mo 3 O 12 -0.4TiO 2 composite ceramic with 1 wt% H 3 BO 3 sintered at 700 °C displays excellent microwave dielectric properties (ε r ∼11.27, Q × f ∼ 43056 GHz, τ f ∼ -3 ppm/°C). It can be served as a pioneering candidate in applications of ULTCC (ultra-low temperature co-fired ceramic). [ABSTRACT FROM AUTHOR]

Solid-phase method was used to synthesize MgMo 1-x W x O 4 (x = 0–0.15) ceramics. The influences of substitution Mo6+ with W6+ on crystal structure, vibration characteristics and microwave dielectric properties of MgMo 1-x W x O 4 ceramics were comprehensively studied. X-Ray diffraction illustrated all samples exhibit single-phase monoclinic wolframite structure when x = 0–0.15, in which W6+ replaces Mo6+ sites formed solid solution. W6+ effectively improves sintering properties of the MgMoO 4 , the average grain size and relative density were increased. Raman characterization reveals that suitable W6+ substitution amount leads to reduction of v 1 A g peaks FWHM and the enhancement of specific v 3 A g peak for Mo/WO 4 tetrahedron, which improves the ordered distribution of the crystal structure. The above combined effect results in the increased Q × f value, but has little influence of W6+ substitution on ε r and τ f for MgMoO 4. When x = 0.09, MgMo 0.91 W 0.09 O 4 ceramic sintered at 1050 °C has optimal microwave dielectric performance: ε r = 7.21, Q ×f = 90,829 GHz, τ f = −67 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: CaO–SiO2–B2O3 (CBS) glass was prepared by water quenching method at low temperature using CaCO3, SiO2, H3BO3, MgO and ZnO as raw materials. The effect of composition on the melting temperature and the effect of TiO2 on the dielectric properties of samples sintered from CBS glass powder were investigated. XRD analysis shows there are no markedly changes between CBS glass and samples sintered from CBS glass. SEM shows that phases in sintered samples were mostly glass phase and little crystal phase. The result shows that the melting temperature of CBS glass can be reduced from about 1450°C to 1100°C; the sintering temperature for this glass-ceramic is 685°C reduced at least by 100°C. The glass-ceramic possesses excellent dielectric properties: dielectric constant (ɛ r) is about 8 and dielectric loss (tan δ) is about 2×10−4 at 25MHz. [Copyright &y& Elsevier]

A single orthorhombic phase Li 2 Mg 2 Mo 3 O 12 ceramic as a novel ultra-low sintering temperature ceramic was investigated and synthesized using a solid-state method. The best sintering temperature was 650 °C, with a high relative density of 97.86%. The structure of the Li 2 Mg 2 Mo 3 O 12 ceramic was characterized by Rietveld refinement, XPS, Raman spectroscopy and FT-IR analysis. The Rietveld refinement and XPS results demonstrated that Mo6+ is located in the near-ideal MoO 4 tetrahedrons, and Mg2+ and Li+ are distributed in the centre of three kinds of AO 6 polyhedrons. The Raman and FT-IR studies confirmed the internal vibrational features of the Li 2 Mg 2 Mo 3 O 12 ceramic. The correlations between the structural and microwave dielectric losses of the Li 2 Mg 2 Mo 3 O 12 ceramic were analysed by Raman spectroscopy. The lower FWHM of the Raman peak indicated lower intrinsic dielectric loss. The Li 2 Mg 2 Mo 3 O 12 ceramic exhibited an optimal microwave dielectric property when sintered at 650 °C: ε r = 9.26, Q × f = 58,583 GHz, and τ f = −51 ppm/°C. Li 2 Mg 2 Mo 3 O 12 ceramic may become a potential material for ULTCC applications. [ABSTRACT FROM AUTHOR]

A series of (1- x) BaWO 4 - x CuO low-temperature sintered composite ceramics were prepared via co-firing the mixture of BaWO 4 and CuO in the first part of this study. The sintering temperature of BaWO 4 was decreased from 1150 °C to 950 °C when a little amount of CuO was used as sintering aids. The 0.95BaWO 4 -0.05CuO sample heated at 950 °C for 4 h had good dielectric performance (Q × f ~ 31,847 GHz, ε r ~ 7.99, τ f ~ −81.7 ppm/°C). However, the negative τ f was too large to apply to practice. To solve this problem, the rutile phase TiO 2 nano-particle with a large positive temperature coefficient of +450 ppm/°C was added as τ f compensator in the second part of the study. TiO 2 powders not merely improved the temperature stability, but promoted the grain growth. However, the ε r value increased from 10.5 to 12.6 and Q×f value decreased slightly as TiO 2 content increased from 0.30 to 0.45. The 0.65 (0.95BaWO 4 -0.05CuO) −0.35TiO 2 composite ceramic displayed an optimum performance (Q × f ~ 22,012 GHz, ε r ~ 11.21, τ f ~ −2.9 ppm/°C). Such a sample was chemically compatible with silver, implying that it can be implemented on LTCC applications. [ABSTRACT FROM AUTHOR]

Ba 1-x Ca x MoO 4 (0 ≤ x ≤ 0.20) ceramics were prepared from powders to form solid solutions by a solid-state reaction sintering process. The influence of the Ca2+ content on the microstructure, sintering, densification, microwave dielectric properties and chemical stability of BaMoO 4 -based ceramics with Ag metal was discussed in detail. The sintering temperatures of the Ba 1- x Ca x MoO 4 ceramics were effectively reduced to less than 950 °C by the formation of the solid solutions. Structural analysis indicates that the Ba 1-x Ca x MoO 4 ceramics belong to the class of tetragonal scheelites. The crystal grain size begins to decrease and become more regular as x increases from 0 to 0.12. However, as x continues to increase, a liquid phase begins to appear, and the grain boundaries are no longer clear. The ε r value increases from approximately 8.6 to 9.8 as x increases from 0 to 0.2. The Ba 0.92 Ca 0.08 MoO 4 sample possesses the best microwave dielectric performance, namely an ε r = 9.3 and the maximum Q × f value of 33593 GHz. The addition of 15 wt% TiO 2 or 10 wt% CaTiO 3 can effectively change the τ f values of the Ba 1-x Ca x MoO 4 ceramics to approximately 0. The Ba 1-x Ca x MoO 4 ceramic samples can coexist with silver during the LTCC cofiring process. [ABSTRACT FROM AUTHOR]

Cr: YAG and Cr, Nd: YAG transparent ceramics have significant application prospects in solid state lasers, therefore a controllable charge state of Cr ion in Cr doped YAG transparent ceramics is necessary. In this study, a successful regulation of Cr charge state in both Cr, Nd: YAG and Cr: YAG transparent ceramics was achieved, by a simple optimizing the sintering additives. Both ceramics with the Cr doping concentration of 0.3 at% reached to the theoretical transmittance, after the vacuum sintering and the subsequent annealing process. It was found that by adopting silica additive, divalent charged Cr 2+ ions could be detected from the vacuum sintered samples, and they were transferred into trivalent state after further annealing in air. Meanwhile, by vacuum sintering ceramics with divalent additives (CaO and MgO), a stable trivalent charged Cr ion could be obtained, and the subsequent air annealing process indicated a significant conversion from Cr 3+ to Cr 4+ . Further increasing the Cr concentration was not benefit to the optical quality as well as the conversion of Cr 3+ ion in Cr, Nd: YAG transparent ceramics. [ABSTRACT FROM AUTHOR]

In current study, various amounts of MgO single dopant was adopted to fabricated high quality transparent YAG ceramics, by utilizing a simple one-step solid state reaction sintering method in vacuum. At a MgO doping amount of only 0.03 wt.%, YAG transparent ceramics with a transmittance of 84.5% at 1064 nm could be obtained, after sintering at 1820 °C for 8 h. The microstructure evolution and optical property of as-fabricated YAG ceramics as a function of MgO doping concentration were systematically investigated. MgO dopant could effectively promote densification of YAG ceramics when the sintering temperature was lower than 1660 °C, and dramatically accelerate its grain growth between 1540 °C and 1660 °C. Further increase the doping amount of MgO would not benefit to the optical quality of YAG ceramics, and the intragranular pores as well as the Mg-riched secondary phase were observed from the MgO heavily doped ceramics. [ABSTRACT FROM AUTHOR]

Tetraethyl orthosilicate (TEOS) was commonly served as a sintering additive to promote the densification of transparent Y 3 Al 5 O 12 (YAG) ceramics. However, Si 4+ that decomposed from TEOS would restrain the conversion of dopants into a higher valence state (e.g., Cr 3+ → Cr 4+ ). In this study, by using divalent sintering additives (CaO and MgO), the colorless and highly transparent YAG ceramics (T = 84.6%, at 1064 nm) were obtained after vacuum sintering at 1840 °C for 8 h and without subsequent annealing in air. An absorption peak centered at ∼320 nm was observed before annealing, and it extended to ∼550 nm after annealing at 1450 °C for 10 h in air. A discoloration phenomenon occurred and more scattering centers were observed with the formation of new [Mg/Ca 2+ F + ] color centers. Air annealing did not improve the optical quality of the as-fabricated YAG ceramics with divalent dopants as sintering additives, owing to the formation of scattering centers. [ABSTRACT FROM AUTHOR]

Submicrometer grain-sized (1.5 µm) yttria ceramics exhibited the remarkable flexural strength enhancement from 28.5 to 165.0 MPa, and equivalent or superior transparency (81.8%, 1064 nm) to that of single crystal under the two-step sintering of 1550–1500 °C and Al 2 O 3 additive amount of only 150 ppm. [ABSTRACT FROM AUTHOR]

High optical quality Y 2 O 3 transparent ceramics with fine grain size were successfully fabricated by air pre-sintering at various temperature ranging from 1500 to 1600 °C combined with a post-hot-isostatic pressing (HIP) treatment using co-precipitated powders as the starting material. The fully dense Y 2 O 3 transparent ceramic with highest transparency was obtained by pre-sintered at 1550 °C for 4 h in air and post-HIPed at 1600 °C for 3 h (the pressure of HIP 200 MPa), and it had fine microstructure and the average grain size was 0.96 μm. In addition, the in-line transmittance of the ceramic reached 81.7% at 1064 nm (1 mm thickness). By this approach, the transparent Y 2 O 3 ceramics with fine grain size (<1.6 μm) were elaborated without any sintering aid. [ABSTRACT FROM AUTHOR]

Abstract: Nd:YAG transparent ceramics were fabricated by a reactive sintering method under vacuum using SiO2, MgO and compound additives (SiO2 and MgO) as sintering aids. The effects of SiO2 and MgO on the microstructure and sintering process of Nd:YAG ceramics were studied. High quality Nd:YAG ceramics with compound sintering aids obtained by vacuum sintering at 1780°C are composed of grains of the size ∼10μm, and their transmittance is 82% at 400nm. It was found the absorption coefficient of 1.0mol% Nd:YAG ceramic was 8.6cm−1 at 808nm and its absorption cross section was calculated to be 6.26×10−20 cm2. [Copyright &y& Elsevier]

Abstract: Neodymium doped YAG transparent ceramics were fabricated by vacuum reactive sintering method using commercial α-Al2O3, Y2O3 and Nd2O3 powders as the starting materials with both tetraethyl orthosilicate (TEOS) and MgO as sintering aids. The morphologies and microstructure of the powders and Nd:YAG transparent ceramics were investigated. Fully dense Nd:YAG ceramics with average grain size of ∼10μm were obtained by vacuum sintering at 1780°C for 8h. No pores and grain-boundary phases were observed. The in-line transmittance of the ceramic was 83.8% at 1064nm. [Copyright &y& Elsevier]

Abstract: The reaction mechanism between hydrous titanium oxide and potassium carbonate at low temperatures was investigated by using XRD, TG, Raman spectra and TEM. In spite of the TiO2/K2O mole ratio in mixtures, the solid state reactions always consisted of two stages. In the first stage (500–640°C), K2Ti3O7 nanocrystallites with layered structure were formed by the direct reaction of TiO2 and K2CO3 which was clearly confirmed by TG studies in CO2 atmosphere. In the second stage (≥640°C), the TiO2/K2O mole ratio in mixtures affected the solid state reaction mechanism remarkably. A new transformation mechanism was found for mixtures with TiO2/K2O mole ratio of 4. The separation between the two stages could be used to control the morphologies and microstructures of potassium titanates by adjusting CO2 partial pressure in atmosphere. [Copyright &y& Elsevier]