Investigation of the microwave dielectric properties of the Li4x/3Zn2−2xTi1+2x/3O4 system by P–V–L theory and vibration spectroscopy

Li_4x/3Zn_2–2xTi_1+2x/3O₄ microwave dielectric ceramics with a spinel phase were prepared via a high-temperature solid-phase method. P–V–L theory, vibration spectra, and XPS were utilized to establish the links between the intrinsic and extrinsic factors and the microwave dielectric properties. According to the characterization, the change in permittivity (ε_r) was ascribed to the increase in the average bond ionicity of Ti–O(Af_iTi-O) and the polar mode of the lattice vibration; the change in quality factor(Q × f) resulted from the change in the Ti–O lattice energy (AU_Ti-O) and existence of oxygen vacancy; the increase in temperature coefficient of the resonance frequency (τ_f) was triggered by the increase in the Ti–O bond energy. The Li_0.6Zn_1.1Ti_1.3O₄ ceramics (x = 0.45) sintered at 1125 °C finally obtained optimal microwave dielectric constants of ε_r = 17.3, Q × f = 76,318 GHz and τ_f = -58 ppm/°C.     

Stress–corrosion cracking by indentation techniques of a glass coating on Ti6Al4V for biomedical applications

The fixation of bone replacement implants to the hosting tissue can be improved if the implants have a bioactive surface that can precipitate hydroxyapatite in vivo. Titanium alloys, despite their desirable mechanical and nontoxic properties, are not bioactive and do not bond directly to the bone. One of the ways to change a bioinert metallic surface such as a titanium alloy is to coat it with a bioactive material. This work presents the microstructural and stress–corrosion cracking characterization of two glass coatings on Ti6Al4V with different SiO₂ contents (61% and 64%). These coatings belong to the SiO₂–CaO–MgO–Na₂O–K₂O–P₂O₅ system and they were obtained by a simple enamelling technique. They will be used as the first layer of a bioactive multilayer system which will have an outer layer with a lower SiO₂ content in order to ensure the surface bioactivity. Microstructural characterization performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) shows that the coating porosity is clearly influenced by the firing time because of the longer extension of the reaction between Ti and SiO₂. The X-ray diffraction (XRD) integration method shows that the amount of crystalline phase (2.4CaO 0.6Na₂O P₂O₅) percentage is between 3 vol.% and 16 vol.%. After acid etching, a microstructure with clear boundaries is observed which is the result of the sintered glass particles separation. Stress–corrosion cracking was evaluated using Vickers and Hertzian (spherical) indentation, showing that both coatings are sensitive to subcritical crack growth, and that the coating with the lower silica content is more sensitive to stress–corrosion cracking. These two results are related with the larger residual stresses due to the thermal expansion mismatch. Finally, the stress–corrosion ring cracking behavior by Hertzian indentation is rationalized from the linear-elastic fracture mechanics framework.     

Novel high-entropy microwave dielectric ceramics Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 with excellent temperature stability and mechanical properties

Novel high-entropy Sr(La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)AlO₄ ceramics with a layered perovskite structure have been prepared via the standard solid-state reaction method. The design of high-entropy improves the bond valence and subsequently optimizes the large negative temperature coefficient of resonant frequency (τ_f = ?32 ppm/°C) of the simple SrLaAlO₄ ceramics. Excellent temperature stability (τ_f = ?6 ppm/°C) together with a relative permittivity (ε_r) of 18.6 and a quality factor (Qf = 14,509 GHz) are obtained in Sr(La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)AlO₄ ceramics sintered at 1475 °C. It indicates that the present ceramics have great application prospects in passive microwave components such as resonators and filters. Meanwhile, significant improvements in compressive strength and strain are achieved, which are 1040 MPa and 15.7% for Sr(La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)AlO₄ compared to 583 MPa and 12% in SrLaAlO₄. The enhanced mechanical properties originate from the dislocation strengthening mechanism as the intertwining of interlayer lattices is revealed from the high-resolution transmission electronic micrographs.     

Correlation between microstructure and properties of biocomposite coatings

A SiO₂–CaO–Na₂O (SCN) based bioactive glass was used to prepare glass–matrix/Ti particle composite coatings (SCNT). The coatings were obtained by vacuum plasma spray (VPS) on Ti–6Al–4V substrates. Two different deposition methods have been compared: (a) VPS of powders obtained by ball milling of sintered composites; (b) in situ plasma spray of mixed titanium and glass powders. For comparative purposes, pure SCN glass coatings were produced. The coating morphology and microstructure were observed by optical and scanning electron microscopy, compositional analyses by energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Comparative mechanical tests were carried out by shear tests and by Vickers indentations at the interface between the substrate and the coatings. The bioactivity of glass- and composite coatings was investigated in vitro by soaking them in a simulated body fluid (SBF) with the same ion concentration of the human plasma. All the layers retain their starting composition. The composite coatings obtained by VPS of the powdered presintered composites showed a better mechanical behaviour with respect both to the composite coatings obtained by the in situ method and to the pure glass coatings. Both the glass- and the two kind of composite coatings revealed to be bioactive by the growth of a thick apatite layer after 30 days of soaking in SBF. The electrochemical behaviour of the SCNT coatings was evaluated by means of potentiodynamic anodic polarization curves and free corrosion potential measurements in Ringer solution at 25 °C. For comparative purposes the same analyses were performed on analogous bioactive glass-matrix/Ti particle composite coated samples, based on the system TiO₂–SiO₂–CaO–B₂O₃ (TSCB), and obtained both by the in situ and by presintering method as well. The results of the electrochemical tests showed a better corrosion behaviour of the samples coated by VPS of powdered sintered composites with respect to those coated by in situ VPS composites.     

Crystal structures,bond characteristics,and dielectric properties of novel middle-εr Ln3NbO7 (Ln = Nd,Sm) microwave dielectric ceramics with opposite temperature coefficients

This study synthesized two novel middle-ε_r Ln₃NbO₇ (Ln = Nd, Sm; named NNO and SNO) microwave dielectric ceramics through the classic solid-state process. The results of XRD and Rietveld refinement show that NNO and SNO ceramics formed pure phases with the space group Cmcm (63) and C222₁ (20), respectively. The properties of Ln-O and Nb–O bonds of NNO and SNO ceramics were calculated based on the P–V–L theory. The Nb–O bonds positively affect the crystal structure stability of the two ceramics. The optimum microwave dielectric properties were obtained (NNO: ε_r = 31.61, Q·f = 6,615 GHz (at 6.10 GHz), and τ_f = ?455.70 ppm/°C; SNO: ε_r = 34.55, Q·f = 11,625 GHz (at 5.77 GHz) and τ_f = 72.59 ppm/°C) when the samples sintered at 1550 °C. Notably, SNO ceramic shows a low dielectric loss and medium dielectric constant, and the opposite τ_f of NNO and SNO ceramics provide the possibility to fabricate microwave dielectric devices with good temperature stability.     

In vitro characterisation of plasma-sprayed apatite/wollastonite glass–ceramic biocoatings on titanium alloys

Some ceramics have the ability to form direct bonds with surrounding tissues when implanted in the body. Among bioactive ceramics, the apatite/wollastonite (A/W) glass–ceramic, containing apatite and wollastonite crystals in the glassy matrix, has been largely studied because of good bioactivity and used in some fields of medicine, especially in orthopaedics and dentistry. However, medical applications of bioceramics are limited to non-load bearing applications because of their poor mechanical properties. In this study, A/W powders, obtained from industrial and high grade quality raw materials, were thermally sprayed by APS (atmospheric plasma spraying) on Ti–6Al–4V substrates, in order to combine the good bioactivity of the bioceramic and the good mechanical strength of the titanium alloy base material. The microstructure and the resulting properties were evaluated depending on processing parameters and post-processing thermal treatments. The morphology and the microstructure of the coatings were observed by SEM and the phase composition was examined by X-ray diffraction. The bioactivity of the coatings was evaluated by soaking the samples in a simulated body fluid (SBF) for 1, 2 and 5 weeks. The bioactive behaviour was then correlated with the thermal treatments and the presence of impurities (in particular Al₂O₃) in the coatings.     

Electrochemical and structural evaluation of functionally graded bioglass-apatite composites electrophoretically deposited onto Ti6Al4V alloy

Titanium and its alloys are widely used as materials for implants, owing to their corrosion resistance, mechanical properties and excellent biocompatibility. However, clinical experience has shown that they are susceptible to localised corrosion in the human body causing the release of metal ions into the tissues surrounding the implants. Several incidences of clinical failures of such devices have demanded the application of biocompatible and corrosion resistant coatings and surface modification of the alloys. Coating metallic implants with bioactive materials is necessary to establish good interfacial bonds between the metal substrate and the bone. Hence, this work aimed at developing a bioglass-apatite (BG-HAP) graded coating on Ti6Al4V titanium alloy through electrophoretic deposition (EPD) technique. The coatings were characterized for their properties such as structural, electrochemical and mechanical stability. The electrochemical corrosion parameters such as corrosion potential (E_corr) (open circuit potential) and corrosion current density (I_corr) evaluated in simulated body fluid (SBF) have shown significant shifts towards noble direction for the graded bioglass-apatite coated specimens in comparison with uncoated Ti6Al4V alloy. Electrochemical impedance spectroscopic investigations revealed higher polarisation resistance and lower capacitance values for the coated specimens, evidencing the stable nature of the formed coatings. The results obtained in the present work demonstrate the suitability of the electrophoretic technique for the preparation of graded coating on Ti6Al4V substrates.     

A tough graphene nanosheet/hydroxyapatite composite with improved in vitro biocompatibility

Mechanical properties and in vitro biocompatibility of graphene/hydroxyapatite (HA) composite synthesized using spark plasma sintering (SPS) are reported in this study. Raman spectroscopy corroborated that graphene nanosheets (GNSs) survived the harsh processing conditions of the selected SPS processing parameters. A 1.0 wt.% GNS/HA composite exhibits ∼80% improvement in fracture toughness as compared to pure HA. GNS pull-out, grain bridging by GNS, crack bridging and crack deflection are the major toughening mechanisms that resist crack propagation. In vitro osteoblast growth tests illustrate that the added GNSs contribute to the improvement of both osteoblast adhesion and apatite mineralization. Therefore, the GNS/HA composite is expected to be a promising material for load-bearing orthopedic implants.     

Ilmenite-type MgTiO3 ceramics by complex (Mn1/2W1/2)4+ cation co-substitution producing improved microwave characteristics

In this article, the (Mn_1/2W_1/2)⁴⁺ complex cation co-doped ilmenite MgTiO₃ 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_1/2W_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_g⁵ 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_1/2W_1/2)_0.01O₃ 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.     

Relationship between bond characteristics and microwave dielectric properties of REVO4 (RE = Yb,Ho) ceramics

Two novel low-ε_r REVO₄ (RE = Yb, Ho) microwave dielectric ceramics with the symmetry of the zircon structure, space group I4₁/amd, were prepared using the solid-state method. Dense REVO₄ (RE = Yb, Ho) ceramics sintered at 1200 °C and 1160 °C performed ε_r ～ 12.3 ± 0.1 and 13.3 ± 0.1, Q × f ～ 28,200 ± 300 GHz and 24,100 ± 300 GHz, τ_f ～ ?18.8 ± 0.5 ppm/°C and ?17.4 ± 0.5 ppm/°C, along with thermal expansion coefficient (α_L) of 9.0 ppm/°C and 8.1 ppm/°C, respectively. Bond valence results indicated that the slightly rattling RE³⁺ cations at the A-site and compressed V⁵⁺ at the B-site occurred in both ceramics. The positive deviations (Δε_r) of porosity corrected ε_r(Corr) from those calculated by the Clausius-Mosotti equation ε_r(C-M), 8.1% for YbVO₄ and 17.7% for HoVO₄, were observed, implying that the rattling effect of RE³⁺ in dodecahedral A-site were greater than those of compressed V⁵⁺ in tetrahedral B-site. Rattling effect also led REVO₄ (RE = Yb, Ho) to develop higher ε_r, and smaller τ_ε and τ_αm, then closer to zero τ_f values than other zircon-structured REVO₄ (RE = Ce, Nd, Sm, Eu) ceramics with large negative τ_f. The differences in sintering temperature and microwave dielectric performance of both ceramics were discussed using the packing fraction, full width at half maximum (FWHM) of Raman modes and Phillips-Van Vechten-Levine (P–V-L) theory.     

Effects of heat treatment on microstructure and mechanical properties of TiC/TiB composite bioinert ceramic coatings in-situ synthesized by laser cladding on Ti6Al4V

To improve the wear resistance of titanium alloy, in this work, TiC/TiB composite bioinert ceramic coatings were synthesized in-situ via laser cladding using Ti and B₄C mixed powders as precursor materials. And to decrease the impact of the excessive residual tensile stress generated by the uneven temperature distribution on the performance of coatings, the coatings were then subsequently heated for 3 h at different temperatures (400 °C, 600 °C, and 800 °C) and then air cooled. The effects of heat treatment on the microstructure, residual stress, micro-hardness, fracture toughness, and wear resistance of the coatings were investigated. The results showed that phase compositions and microstructure of the heat-treated coatings were virtually identical to that of the untreated coatings; however, the precipitation of acicular TiB enhanced mechanical properties of the heat-treated coatings. In addition, the average residual tensile stress values of the coatings decreased as the heat treatment temperature increased, which improved fracture toughness of the coatings from 3.95 to 4.68 MPa m^1/2. Moreover, wear resistance of the coatings was greatly enhanced by heat treatment; as the wear volume of the heat-treated coatings decreased by 50% at 800 °C compared with that of the untreated coatings. Lastly, the coatings showed good biocompatibility after being evaluated in vitro, and therefore had broad application prospects in the field of orthopedic implants.     

Sol-gel derived nanosized Sr5(PO4)2SiO4 powder with enhanced in vitro osteogenesis and angiogenesis for bone regeneration applications

Bioactive glass ceramics are widely used for hard tissue repair and bone regeneration due to their most attractive properties such as biocompatibility, bioactivity and non toxicity. In this study, for the first time, sol-gel method was used to synthesize nanosized strontium phosphosilicate (SPS: Sr₅(PO₄)₂SiO₄) with rod shaped morphology by using CTAB as a surfactant. The obtained SPS powder was characterized by FTIR, XRD, Raman, SEM-EDS and TEM analysis. In vitro bioactivity study confirms that SPS possesses bone bonding ability by formation of amorphous apatite layer on its surface. In vitro osteogenesis and angiogenesis studies were performed on SPS powder to determine its biological responses using mBMSCs and HUVECs, respectively. The co-culture of BMSCs with different concentrations of SPS powder (50, 100, 150, 200 and 250?µg/ml) reveals that there's no any cytotoxicity effect on mBMSCs and observed good cell proliferation, alkaline phosphatase activity, calcium nodules formation, osteogenesis-related gene expressions (alp, runx2, col1a2 and ocn). In addition, the angiogenesis study demonstrated that SPS powder can stimulate the cellular response of HUVECs and its gene expressions (vegfr2 and hif1α-3). Therefore, these results confirm that nanosized SPS could act as promising bioceramic material for bone tissue engineering applications.     

Cerium-doped hydroxyapatite/collagen coatings on titanium for bone implants

The novelty of the present research consists in the possibility of obtaining cerium-doped hydroxyapatite/collagen coatings on the titanium support, to improve the performance of the bone implants. These coatings were deposited on the titanium surface by biomimetic method using a modified supersaturated calcification solution (SCS) additionally containing a cerium source and collagen. Prior to the deposition of the apatite layer, an alkali ÷ thermal oxidation pretreatment has been applied to ensure an increase in the bioactivity of the titanium surface. The coatings were examined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. The EDX and XRD investigations of the coatings indicated that cerium was incorporated in the hydroxyapatite lattice. The collagen presence in the coatings was confirmed by FTIR analysis. The cerium-doped hydroxyapatite/collagen coatings showed good antibacterial efficacy against Escherichia coli and Staphylococcus aureus bacteria, being more effective against Escherichia coli. These coatings have a significant potential to be used in the dental and orthopedic implants, as the osseointegration depends on much more factors than simple formation of hydroxyapatite.     

Silicon-Doped Titanium Dioxide Nanotubes Promoted Bone Formation on Titanium Implants

While titanium (Ti) implants have been extensively used in orthopaedic and dental applications, the intrinsic bioinertness of untreated Ti surface usually results in insufficient osseointegration irrespective of the excellent biocompatibility and mechanical properties of it. In this study, we prepared surface modified Ti substrates in which silicon (Si) was doped into the titanium dioxide (TiO₂) nanotubes on Ti surface using plasma immersion ion implantation (PIII) technology. Compared to TiO₂ nanotubes and Ti alone, Si-doped TiO₂ nanotubes significantly enhanced the expression of genes related to osteogenic differentiation, including Col-I, ALP, Runx2, OCN, and OPN, in mouse pre-osteoblastic MC3T3-E1 cells and deposition of mineral matrix. In vivo, the pull-out mechanical tests after two weeks of implantation in rat femur showed that Si-doped TiO₂ nanotubes improved implant fixation strength by 18% and 54% compared to TiO₂-NT and Ti implants, respectively. Together, findings from this study indicate that Si-doped TiO₂ nanotubes promoted the osteogenic differentiation of osteoblastic cells and improved bone-Ti integration. Therefore, they may have considerable potential for the bioactive surface modification of Ti implants.     

Structure and microwave dielectric properties of novel walstromite-type MCa2Si3O9 (M = Ba,Sr) ceramics

Novel walstromite-type MCa₂Si₃O₉ (M = Ba, Sr) ceramics, with triclinic space group P-1, were prepared through a solid-state reaction method. The P–V-L theory proves that the lattice energy and bond energy of the Si–O bond play a leading role in the quality factor and the dielectric constant is mainly determined by the ionic polarization. Excellent microwave dielectric properties of BaCa₂Si₃O₉ and SrCa₂Si₃O₉ ceramics could be obtained: ε_r = 8.99 ± 0.23, Q × f = 44,542 ± 500 GHz, and τ_f = −25.9 ± 3.0 ppm/°C and ε_r = 7.39 ± 0.23, Q × f = 48,772 ± 500 GHz, and τ_f = −27.5 ± 3.0 ppm/°C, when sintered at 1240/1280 °C for 4 h. Then SrCa₂Si₃O₉ ceramic is applied to a new microstrip bandpass filter, because of its high microwave dielectric properties and low thermal expansion coefficient. With reduced dimension, the filtering performance of the circuit is also highly improved, including reduced capacitor parasitic effect and the optimized stopband insertion loss. Accordingly, the SrCa₂Si₃O₉ ceramic is a promising candidate for sub-6 GHz a filter of microstrip bandpass applications.     

Ultrafine-grained β-Sialon fabricated by two-stage sintering and study on diffusion toughening of Ti–22Al–25Nb

The ultrafine-grained β-Sialon ceramics were fabricated by spark plasma sintering at different temperatures with inorganic Al₂O₃–Y₂O₃ and Ti–22Al–25Nb intermetallic powder as composite additives. The research showed that β-Sialon ceramics achieve two-stage sintering densification. Al₂O₃–Y₂O₃ inorganic additives promoted the synthesis and densification of β-Sialon ceramics at 1125–1215°C. Ti–22Al–25Nb intermetallic powder diffused Ti and Nb elements at 1240–1425°C, thereby improving the fracture toughness of β-Sialon ceramics. The maximum fracture toughness (∼9.69 MPa m^1/2) under 19.6 N was obtained for β-Sialon ceramics sintered at 1600°C.     

Calcium zirconium silicate (baghdadite) ceramic as a biomaterial

Bioceramics have been widely used for many years to restore and replace hard tissues including bones, teeth and mineralized matrices such as calcified cartilages at osteochondral interfaces, mainly because of their physicochemical similarity with these tissues. Calcium silicate based bioceramics have been shown to possess high bioactivity due to having high apatite-forming ability and stimulating cell proliferation, as well as biodegradability at rates appropriate to hard tissue regeneration. The outstanding biological properties of these ceramics have made them the most studied hard tissue engineering biomaterials along with calcium phosphates and bioactive glasses. Baghdadite is a calcium silicate containing zirconium ions which promotes the proliferation and differentiation of human osteoblasts and consequently increases mineral metabolism and ossification. Recently, it has attracted considerable attention in academic community and widely studied in the form of porous scaffolds, coatings, bone cement and void fillers, microspheres and nanoparticles mostly in orthopedic, dental and maxillofacial applications. This review paper is aimed to summarize and discuss the most relevant studies on the mechanical properties, apatite formation ability, dissolution behavior, and in vitro and in vivo biological properties of baghdadite as a biomaterial for hard tissue regeneration applications.     

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

Microwave dielectric properties of corundum-structured Mg₄Ta₂O₉ 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 Mg₄Ta₂O₉ ceramics were studied as a function of sintering temperature from 1250 °C to 1450 °C. With increasing sintering temperature, the density, ε_r and Qf values increased, saturating at 1300 °C with excellent microwave properties of ε_r=11.9, Qf=195,000 GHz and τ_f=?47 ppm/°C. Evaluation of dielectric properties of Mg₄Ta₂O₉ ceramics were also analyzed by means of first principle calculation method and ionic polarizability theory.     

Low loss and good chemical compatibility with silver electrodes of Cu2+-substituted Ba3Ti4Nb4O21 ceramics realizing low temperature co-fired ceramics technology: Crystal structure,vibration modes and chemical bonds studies

New low loss and low-sintering temperature co-fired Ba_3-xCu_xTi₄Nb₄O₂₁ (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li₂O-B₂O₃-SiO₂-CaO-Al₂O₃ (LBSCA) glass were prepared by solid-state reaction methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with ε_r ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τ_f ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to ε_r. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τ_f closely related to the oxygen octahedron [Ti1/Nb1O₆]. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.     

Temperature-independent permittivity of xBaTiO3–(1−x)(0.5Bi(Mg1/2Ti1/2)O3–0.5BiScO3) ceramics

xBaTiO₃–(1−x)(0.5Bi(Mg_1/2Ti_1/2)O₃-0.5BiScO₃) or xBT–(1−x)(0.5BMT–0.5BS) (x=0.45–0.60) ceramics were prepared by using the conventional mixed oxide method. Perovskite structure with pseudo-cubic symmetry was observed in all the compositions. Dielectric measurement results indicated that all the samples showed dielectric relaxation behavior. As the content BaTiO₃ was decreased from 0.60 to 0.45, temperature coefficient of permittivity (TCε) in the range of 200–400 °C was improved from −706 to −152 ppm/°C, while the permittivity at 400 °C was increased from 1208 to 1613. The temperature stability of permittivity was further improved by using 2 mol% Ba-deficiency. It was found that lattice parameter and grain size of the 2 mol% Ba-deficient ceramics were smaller than those of their corresponding stoichiometric (S) counterparts, with TCε in the range of 200–400 °C to be improved noticeably. For example, TCε of the Ba-deficiency sample with x=0.45 was −75 ppm/°C in the temperature range of 200–400 °C and the permittivity was 1567 at 400 °C. The results obtained in this work indicated that xBT–(1−x)(0.5BMT–0.5BS) ceramics are very promising candidates for high temperature capacitor applications.