Low-fired (1−x)Mg2SiO4–xCa0.9Sr0.1TiO3–4 wt% LiF(0.1 ≤ x ≤ 0.15) composite ceramics were prepared by using nanopowders of Mg2SiO4 and Ca0.9Sr0.1TiO3 derived from high energy ball milling (HEBM). The effects of LiF and Ca0.9Sr0.1TiO3 addition on the sinterability, crystal structure, microstructures and microwave dielectric properties of Mg2SiO4-based ceramics were investigated. The sintering temperature of composite ceramics was effectively reduced due to LiF liquid phase. As the amount of Ca0.9Sr0.1TiO3 increased, the temperature coefficient of resonant frequency (τf) of Mg2SiO4 was adjusted to ~0 ppm/ºC. Well-densified 0.86Mg2SiO4–0.14Ca0.9Sr0.1TiO3–4 wt% LiF composite ceramics sintered at 900 °C showed good microwave dielectric properties of εr = 10.0, Q × f = 61,000 GHz, and τf = −5.96 ppm/ºC. This material is compatible with Ag electrodes and suitable for the low-temperature co-fired ceramics applications.

•Temperature stable Li2Mg3TiO6-SrTiO3 composite ceramics with high Q were prepared.•LiF-doping lowered sintering temperature of LMT-ST ceramics to 900 °C.•The temperature stability was improved by adding ST.•A near zero τf values of 6.5 ppm/°C is obtained for samples for x = 0.1.•Ceramics with well dielectric properties are suitable for LTCC applications.New temperature stable 4 wt% LiF-doped (1-x)Li2Mg3TiO6-xSrTiO3 (LMT-ST, x = 0.05, 0.08, 0.10, 0.15) composite ceramics were fabricated by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. Well-densified LMT-ST composite ceramics were obtained with a relative density of 97.2% at 900 °C. A near zero of τf value was obtained by tuning ST composition. 0.9LMT-0.1ST-4wt% LiF ceramics displayed optimum microwave dielectric properties: εr = 19.5, Q×f = 64290 GHz, τf = 6.5 ppm/°C at 900 °C. Such samples were compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems.

•Ultralow-fired LiF-doped Li2Mg3TiO6-Ca0.8Sr0.2TiO3 composite ceramics were prepared.•LiF Addition lowered sintering temperature of LMT-CST ceramics to 725 °C.•The temperature stability of LMT-CST ceramics was improved by adding CST.•A near zero τf values of 0.3 ppm/°C is obtained for LMT-CST ceramics at 800 °C.•Ceramics with well dielectric properties are suitable for LTCC applications.New temperature stable 4 wt% LiF-doped (1−x)Li2Mg3TiO6-xCa0.8Sr0.2TiO3 (LMT-CST, x = 0.10, 0.15, 0.20, 0.25) composite ceramics were fabricated by solid-state reaction for developing ultra-low temperature (≤800 °C) sintering microwave dielectric ceramics. Sintering temperatures of LMT-CST ceramics were successfully lowered to 725 °C due to LiF liquid-phase sintering and well-densified microstructures were obtained at 800 °C. Excellent microwave dielectric properties of εr = 18.8, Q × f = 48200 GHz (at 8.2 GHz), τf = 0.3 ppm/°C was obtained at 800 °C for 0.8 LMT-0.2CST-4wt% LiF ceramics. Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications.

•Sintering temperature and x have huge influence on dielectric properties of BNTO.•This work indicates that Bi3+ may be conducive to dielectric properties of BNTO.•Some Bi3+ ions substitute for Ti4+ sites and enter the TiO2 lattice.The (Bi0.5Nb0.5)xTi1-xO2 (BNTO, 0 ≤ x ≤ 0.05) ceramics were synthesized by a standard conventional solid-state reaction. The effects of sintering temperature and composition x on the crystal structure, microstructure, and dielectric properties of BNTO ceramics were investigated. A pure rutile phase is achieved as x ≤ 0.01, and secondary phase Bi1.74Ti2O6.624 is detected as x ≥ 0.025. BNTO ceramic with x = 0.025 shows a high dielectric constant (155.1 k) and low dielectric loss (0.042) at 1 kHz (room temperature). Colossal permittivity is primarily related to Maxwell-Wagner effect, electron-pinned defect-dipoles or weak-binding electron. The low dielectric loss is argued to Bi ions which are doped into TiO2 lattice and the formation of Bi1.74Ti2O6.624 phase.

•(1−x)Ca5Mg4(VO4)6-xBa3(VO4)2 composite ceramics prepared via a solid state route.•Near-zero τf for Ca5Mg4(VO4)6-based ceramics were achieved by doping Ba3(VO4)2.•0.35Ca5Mg4(VO4)6-0.65Ba3(VO4)2 ceramics had good microwave dielectric properties.•Ca5Mg4(VO4)6-based ceramics showed good chemical compatibility with silver.(1−x)Ca5Mg4(VO4)6-xBa3(VO4)2 (0.5 ≤ x ≤ 0.7) ceramics were fabricated via the conventional solid-state reaction method. The phase composition, microstructure, and compatibility with silver were investigated using X-ray diffraction, Raman spectra and Scanning electron microscopy. The results confirmed that Ca5Mg4(VO4)6 and Ba3(VO4)2 crystal phases can be well coexisted in the sintered ceramics. The temperature coefficient of resonant frequency could be tuned by the volume mixture rule of Ca5Mg4(VO4)6 and Ba3(VO4)2. As for the addition of Ba3(VO4)2, the εr showed to increase, while the Qxf declined. In particular, the 0.35Ca5Mg4(VO4)6-0.65Ba3(VO4)2 composite ceramics sintered at 900 °C for 5 h showed excellent combinational microwave dielectric properties: εr = 11.9, Qxf = 35 000 GHz, and τf = −2 ppm/°C, which also exhibited good chemical compatibility with silver.

•(Yb1/2Nb1/2)0.05Ti0.95O2 ceramics sintered in oxygen partial pressure 10% ≤ x ≤ 100%.•Average grain size rises from 5 μm to 28 μm with x increasing.•Colossal permittivity (>104) and low loss (<0.1) are achieved.•Dielectric properties of x ≥ 50% remain stable over 120 K–370 K and 100 Hz–100 kHz.•High grain resistivity and breakdown voltage have been obtained.(Yb1/2Nb1/2)0.05Ti0.95O2 ceramics are fabricated by the solid state reaction method. The effects of oxygen partial pressure in the sintering atmosphere (10% ≤ x ≤ 100%) on crystal structures, microstructure and dielectric properties of (Yb1/2Nb1/2)0.05Ti0.95O2 are investigated. All samples have rutile structure, and average grain size rises from 5 μm to 28 μm with x increasing from 10% to 100%. All samples show colossal permittivity (above 104). The dielectric properties of x ≥ 50% samples show well temperature (120 K–370 K) and frequency stability (100 Hz–100 kHz). The grain resistivity of x = 100% sample is three orders of magnitude higher than that of x = 10%. The breakdown voltage improves from 246 to 716 V/cm with increasing oxygen partial pressure. Both the Ti valence and oxygen concentration have been influenced by sintering atmosphere.

•Addition of LiF lowered sintering temperature of Ba(Mg1/2W1/2)O3 ceramics from 1500–1600 °C to 900–975 °C.•Well densified structures with high Q×f values have been obtained.•LiF-doped Ba(Mg1/2W1/2)O3–TiO2 composite ceramics were produced.•A near zero τf value was obtained at 950 °C for 0.96 Ba(Mg1/2W1/2)O3–0.04 TiO2–4.0 wt% LiF ceramic.•These ceramics were compatible with Ag electrodes.The Ba(Mg1/2W1/2)O3 (BMW)–x wt% LiF (x = 2.0, 4.0, 6.0, 8.0) ceramics were prepared by a conventional solid-state route. The effects of LiF addition on the sinterability, crystal structure, microstructures and microwave dielectric properties of BMW ceramics were investigated. With an amount of LiF addition, the sintering temperature of the ceramics was reduced to below 960 °C from 1550 °C without degradation of microwave dielectric properties, due to the enhancement of the apparent density at low temperature by liquid phase sintering. On this basis, TiO2 was used to adjust the temperature coefficient of resonant frequency, optimized microwave dielectric properties with εr = 20, Q×f = 48,000 GHz, and τf = 1.2 ppm/°C for 0.96 BMW–0.04 TiO2–4.0 wt% LiF composition. With low sintering temperature and good dielectric properties, these LiF-doped ceramics are promising materials for LTCC integration applications.The novel (1−y) Ba(Mg1/2W1/2)O3–y TiO2–x wt% LiF composite ceramics sintered at 950 °C exhibited excellent microwave dielectric properties of εr = 20, Q × f = 48,000 GHz, and τf = 1.2 ppm/°C for x = 4.0 and y = 0.04 composition.

Li2MnO3 ceramics co-doped with 2 wt% LiF and x wt% TiO2 (x=0, 3, 5, 7, 10) were prepared by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. The sintering temperatures of Li2MnO3 ceramics were successfully lowered to 925°C due to the formation of a LiF liquid phase. Their temperature stability was improved by doping with TiO2. A typical Li2MnO3-2 wt% LiF-5 wt% TiO2 sample with well-densified microstructures displayed optimum dielectric properties (εr=13.8, Q×f= 23,270 GHz, τf=1.2 ppm/°C). Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems.

Using a conventional solid-state reaction Li2Mg3BO6 (B = Ti, Sn, Zr) ceramics were prepared and their microwave dielectric properties were investigated. The analysis revealed that cubic Li2Mg3BO6 (B = Ti, Sn, Zr) ceramics with a rock salt structure could be obtained in their respective sintering temperature range. Three promising ceramics Li2Mg3TiO6, Li2Mg3SnO6 and Li2Mg3ZrO6 sintered at 1280 °C, 1360 °C and 1380 °C possessed out-bound microwave dielectric properties: ϵr = 15.2, 8.8 and 12.6, Q × f = 152,000 GHz (at 8.3 GHz), 123,000 GHz (at 10.7 GHz) and 86,000 GHz (at 9.3 GHz), and τf = −39 ppm/°C, −32 ppm/°C and −36 ppm/°C, respectively.

•A novel microwave dielectric ceramic LiAlW2O8 was prepared by solid-state route.•These ceramics have ultra-low sintering temperature with 740–800 °C.•These ceramics exhibited near-zero temperature coefficient of resonant frequency (τf).A novel temperature stable microwave dielectric ceramic LiAlW2O8 was prepared by a conventional solid-state reaction method with a low temperature range from 740 °C to 800 °C. A monoclinic structure was observed for LiAlW2O8 ceramic coupled with a minor of second unknown phase. The ceramics could be well sintered at 780 °C for 4 h with 95.6% relative density and exhibited excellent microwave dielectric properties with permittivity (εr) of 11.7, Q×f value of 23,000 GHz (at 9.0 GHz), and temperature coefficient of resonant frequency (τf) of −5.3 ppm/°C.The novel LiAlW2O8 microwave dielectric ceramic could be well densified at 780 °C for 4 h and exhibited excellent microwave dielectric properties of εr=11.7, Q×f=23,000 GHz, and τf=−5.3 ppm/°C.

The ZnO–Nb2O5–xTiO2 (1 ≤ x ≤ 2) ceramics were fabricated by reaction-sintering process, and the effects of TiO2 content and sintering temperature on the crystal structure and microwave dielectric properties of the ceramics were investigated. The XRD patterns of the ceramics showed that ZnTiNb2O8 single phase was formed as x ≤ 1.6 and second phase Zn0.17Nb0.33Ti0.5O2 appeared at x ≥ 1.8. With the increase of TiO2 content and sintering temperature, the amount of the second phase Zn0.17Nb0.33Ti0.5O2 increased, resulting in the increase of dielectric constant, decrease of Q × f value, and the temperature coefficient of resonant frequency (τf) shifted to a positive value. The optimum microwave dielectric properties were obtained for ZnO–Nb2O5–2TiO2 ceramics sintered at 1075 °C for 5 h: εr = 45.3, Q × f = 23,500 GHz, τf = +4.5 ppm/°C.

(In1/2Nb1/2)TiO2 (IN-T) ceramics were prepared via a solid-state reaction route. X-ray diffraction (XRD) and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compounds. The results indicated that the sintered ceramics have a single phase of rutile TiO2. Dielectric spectroscopy (frequency range from 20 Hz to 1 MHz and temperature range from 10 K to 270 K) was performed on these ceramics. The IN-T ceramics showed extremely high permittivities of up to ∼103, which can be referred to as colossal permittivity, with relatively low dielectric losses of ∼0.05. Most importantly, detailed impedance data analyses of IN-T demonstrated that electron-pinned defect-dipoles, interfacial polarization and polaron hopping polarization contribute to the colossal permittivity at high temperatures (270 K); however, only the complexes (pinned electron) and polaron hopping polarization are active at low temperatures (below 180 K), which is consistent with UDR analysis.

Correction for ‘Origin of colossal permittivity in (In1/2Nb1/2)TiO2via broadband dielectric spectroscopy’ by Xiao-gang Zhao et al., Phys. Chem. Chem. Phys., 2015, 17, 23132–23139.

•HEBM method synthesized the Mg2TiO4 powders with average size 163 nm.•The highly reactive nanosized pure Mg2TiO4 powders were obtained at low temperature about 1000 °C.•The Mg2TiO4 ceramics sintered at low temperature about 1175 °C showed excellent microwave dielectric properties.Mg2TiO4 ceramics were prepared with MgO and TiO2 by high energy ball milling method. Highly reactive nanosized Mg2TiO4 powders were successfully synthesized at 1000 °C in oxygen atmosphere for milled 30 h, about 200 °C lower than that by a conventional solid-state reaction process. The pure Mg2TiO4 nanopowders average particle size were reduced to about 163 nm. Mg2TiO4 ceramics at 1175 °C had the excellent microwave dielectric properties ɛγ = 13.9, Q × f = 98,600 GHz, τf = −50.9 ppm/°C.

Rock-salt-structured Li2MgTiO4 ceramic was prepared by the conventional solid-state route, and sintered at 1200–1300 °C for 5 h. The sintering behavior, microstructures and microwave dielectric properties of the Li2MgTiO4 ceramic have been investigated. The structure and microstructure were analyzed by using X-ray diffraction and scanning electron microscopy techniques. The secondary phases of Mg2TiO4 and Li2Mg3Ti4O12 were produced, when sintering temperatures exceeded 1250 °C. The dielectric properties of the Li2MgTiO4 ceramic exhibited a significant dependence on the densification and secondary phases. The Li2MgTiO4 ceramics sintered at 1250 °C showed good microwave dielectric properties: εr=15.7, Q×f=91,000 (at 8.1 GHz), and τf=−28 ppm/°C.

•Li2TiO3 nanopowders are prepared at 600 °C by using high-energy ball milling route.•The average particle size of Li2TiO3 powders is 86.7 nm.•Decreasing particle size of powders decreases the sintering temperature of ceramics.•Li2TiO3 ceramics are obtained at 1000 °C by using nanopowders as a precursor.•Increasing density will increase microwave dielectric properties of ceramics.In this study, Li2TiO3 nanopowders were synthesized via a high-energy ball-milling process followed by calcinations and Li2TiO3 ceramics were fabricated by solid-state reaction. The microstructure and microwave dielectric properties of Li2TiO3 ceramics were also investigated systematically. Li2TiO3 nanopowders with an average particle size of 86.7 nm were derived at 600 °C for 2 h. X-ray diffraction patterns exhibited that single monoclinic structure of the Li2TiO3 ceramics were obtained at an optimum sintering temperature of 1000 °C for 2 h by using low temperature synthesis nanopowders as a precursor. The samples of Li2TiO3 ceramics with grain sizes in the range of 1.5–5.0 μm showed dense microstructures and excellent microwave dielectric properties (ɛr = 16.4, Q × f = 54,326 GHz, τf = 27.4 ppm/°C). All these results illustrated that high-energy ball-milling method is a simple and practical route to produce Li2TiO3 ceramics for microwave applications.

•The thermal expansion behavior is opposite in poled and unpoled PMN–31PT crystal.•Two additional structural modifications are detected in the unpoled crystal.•The thermal expansion reveals the cT > cR and cT > cC in unpoled PMN–31PT crystal.•The M phase is detected in thermal expansion curve of poled PMN–31PT crystal.•The T–C phase transition temperature of unpoled crystal is higher than that of poled.The thermal expansion and phase transition of unpoled and poled [0 0 1]-oriented 0.69Pb(Mg1/3Nb2/3)O3–0.31PbTiO3 crystals are investigated using thermomechanical analysis, domain evolution, and dielectric measurement. Results of thermomechanical analysis show that the unpoled crystal exhibits negative thermal expansion at a temperature range from 30 °C to 120 °C, and the lattice parameter c of the tetragonal (T) phase is larger than those of the rhombohedral (R) and cubic (C) phases, i.e., cT > cR and cT > cC. Two additional structural modifications near 50 °C and 125 °C are detected in the unpoled crystal. Compared with that of the poled crystal, the T → C phase transition temperature of the unpoled crystal is relatively higher. An increase in temperature causes the unpoled crystal to undergo R → T → C phase transition, whereas R → M → T → C phase transition sequences are observed in the poled crystal. The phase transition behaviors are further verified by domain evolution and dielectric measurement. The significant differences between poled and unpoled crystals are attributed to the differences in their domain structures.

A novel low temperature firing high Q microwave dielectric ceramic Ca5Co4(VO4)6 was prepared by the conventional solid-state reaction method. The phase purity, microstructure, and microwave dielectric properties were investigated. The Ca5Co4(VO4)6 ceramic sintered at 875 °C exhibited excellent microwave dielectric properties: Qxf = 95,200 GHz (at 10.6 GHz), τf = −63 ppm/°C, ɛr = 10.1, and its ɛr corrected for porosity was calculated as 11.1.

(Bi1/2Na1/2)0.94Ba0.06TiO3 (BNBT6) ceramics with 3 wt.% Bi2O3 and xwt.%Nd2O3 (x = 0, 1.5, 4.5, 6.0) doping were prepared by solid state reaction. The phase transition behaviors and electric properties of ceramics were investigated. The results showed that with doping of 3 wt.% Bi2O3, an antiferroelectric (AFE) phase was induced in ferroelectric BNBT6 ceramics at room temperature. It was attributed to disruption of the ferroelectric coupling between [BO6] octahedra since the generation of A-site vacancies. The AFE (Bi1/2Na1/2)0.94Ba0.06TiO3-3wt.%Bi2O3 (BNBT6-3B) ceramics showed a high phase transition temperature (Tm ~ 320 °C), corresponding to the AFE - paraelectric (PE) phase transition. Low Nd2O3 (x = 1.5, 4.5) doping was helpful to strengthen the AFE phase of BNBT6-3B, while high Nd2O3 (x = 6.0) resulted in a stronger frequency dispersion due to the enhancement of A-site cation disorder. With increasing temperature, the ceramics with low Nd2O3 underwent a relaxor AFE - AFE - PE phase transition, while only relaxor AFE - PE phase transition was presented in high Nd2O3-doped ceramics. An excellent dielectric properties (εmax = 2916) was obtained in x = 1.5 sample.

•Cerium modified KNBT ceramics were synthesized using the solid-state process.•The d33 and ρ of KNBT ceramic were improved by cerium additives.•The tan δ at high temperature of KNBT ceramic was suppressed by cerium additive.•The d33 and Tc of KNBT-Ce50 ceramic were 28 pC/N and 656 °C, respectively.The effect of cerium additive on structure and electric properties of Aurivillius oxide (K0.16Na0.84)0.5Bi4.5Ti4O15 (KNBT), was investigated. Phase analysis was performed by X-ray diffraction analyses (XRD) and Raman spectroscopy. Morphologies were assessed by the scanning electron microscopy. Piezoelectric properties of the KNBT ceramic were improved by the modification of cerium ions. Dielectric loss at high temperature of the KNBT ceramic was also suppressed because of the cerium ions introduced. Piezoelectric coefficient (d33) and Curie temperature (Tc) of KNBT ceramic modified with 0.50 wt% cerium were 28 pC/N and 656 °C, respectively, together with higher resistivity (higher than 107 Ω cm at 550 °C). Moreover, reasons for the improvement of electric properties of the KNBT ceramic modified by cerium were also discussed.

Highly reactive amorphous SiO2 nanospheres were successfully synthesized at room temperature in atmosphere with a mean particle size of 174 nm by a Sol–Gel method. SiO2 ceramics were prepared using SiO2 nanospheres and their microwave dielectric properties were investigated at different temperatures. Phase evolution, sintering characteristics and microstructures were detected by differential thermal analysis (DTA-TG) analysis, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Excellent microwave properties of εr ∼ 3.52, Q·ƒ ∼ 92400 GHz and τƒ ∼ −14.5 ppm/°C, were obtained finally. The optimum sintering temperature of SiO2 ceramics was reduced 125 °C by aqueous Sol–Gel process compared to a conventional solid-state method. The Q·ƒ and εr values of SiO2 ceramics are sensitive to the measured temperatures, which was explained by a simple composite dielectric model.Highlights► Highly reactive amorphous SiO2 nanospheres were synthesized at room temperature by a Sol–Gel method. ► SiO2 nanospheres were used to preparation of SiO2 ceramics and Excellent microwave properties of εr ∼ 3.52, Q ƒ ∼ 92400 GHz and τƒ ∼ −14.5 ppm/°C, were obtained. ► The optimum sintering temperature of SiO2 ceramics was reduced 125 °C compared to a conventional solid-state method. ► The Q·ƒ and εr values of SiO2 ceramics are sensitive to the measured temperatures, which was explained by a composite dielectric model.

•The AWO4 nanopowders with a single phase were synthesized by HEBM for 30 min.•The average particle size of the milled powders is reduced to 120–180 nm for 30 h.•AWO4 ceramics were well sintered at relatively low temperatures of 900–1000 °C.•Samples have dense microstructures and excellent microwave dielectric properties.The AWO4 (A = Ca, Sr, Ba) compounds with scheelite structure were synthesized by high energy ball milling for 30 min and the average particle size was reduced to about 120 nm after milling 30 h. AWO4 ceramics were well sintered at relatively low temperatures of 900–1000 °C, 200–400 °C lower than those required by a conventional solid state reaction technique. The samples of CaWO4, SrWO4, and BaWO4 ceramics have dense microstructures and excellent microwave dielectric properties, ɛr = 10.7, 8.6, 8.4; Q × f = 62,100 GHz, 57,500 GHz, 58,800 GHz; and τf = −48 ppm/°C, −52 ppm/°C, −64 ppm/°C, respectively.

Li2MgTi3O8 ceramics were prepared by reaction-sintering method (free calcination) for the first time and its microwave dielectric properties were investigated. A single phase of Li2MgTi3O8 ceramic was confirmed by XRD pattern. The variation of microstructures was analyzed by SEM. With increasing sintering temperature, the bulk density decreased, the εr and Q × f increased firstly and then decreased, while the τf changed slightly and remained around 1.5 ppm/ °C. In particular, Li2MgTi3O8 ceramics sintered by reaction-sintering method at 1100 °C for 5 h exhibited fine combination microwave dielectric properties of εr = 23.0, Q × f = 54 052 GHz (at 7.29 GHz) and τf = 1.5 ppm/ °C.

(1 − x)Bi0.5Na0.5TiO3–x(Ba0.7Ca0.3)TiO3 (BNT–xBCT, 0 ≤ x ≤ 0.15) solid solutions have been synthesized by a conventional solid state sintering method for obtaining a morphotropic phase boundary (MPB) with good piezoelectric properties. X-ray diffraction patterns reveal that a MPB of rhombohedral and tetragonal phases is formed at compositions 0.09 ≤ x ≤ 0.12. Addition of BCT into BNT greatly lowered coercive field Ec without degrading remanent polarization Pr. The specimen with x = 0.09 has the good piezoelectric properties: d33 = 125 pC/N and kp = 0.33. A modified Curie–Weiss law was used to fit the dielectric constant of BNT–xBCT ceramics, and a frequency dispersion was observed during the phase transitions from antiferroelectric to paraelectric in specimens with x exceeding 0.06.

For the purpose of multilayer chip electromagnetic interference (EMI) filters, a series of xBa0.6Sr0.4TiO3 (BST) + (1 − x)Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98 (NiCuZn ferrite) (0 ≤ x ≤ 60 wt.%) composite ceramics were primarily prepared by a solid-state reaction method. With addition of 3 wt.% Bi2O3, all the composite ceramics can be sintered to a density >95% of theoretical density at 925 °C. The effects of composition x on the sintering behaviors, phase compositions and electromagnetic properties of BST + NiCuZn ferrite composite materials were investigated. X-ray diffraction (XRD) results showed that the composites were composed of BST and NiCuZn phases. The ions’ diffusion was found to take place between NiCuZn ferrite and BST, which affected the electrical properties of the ceramics. With an increase of BST content x, the dielectric constant of the composites increases and the permeability decreases. For the specimens with 40 wt.% Ba0.6Sr0.4TiO3–60 wt.% Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98, the good dielectric (ɛr = 48, tan δ|ɛ = 0.01) and magnetic properties (μ = 20.8, tan δ|10 MHz = 0.03) have been obtained at 950 °C. Meanwhile, it exhibited excellent frequency stability which was up to fr = 100 MHz.

The effects of high-energy ball milling and subsequent calcinations on the mixture of MgO and Nb2O5 were investigated. It was found that the formation temperature of the single-phase Mg4Nb2O9 powders had a consanguineous connection with milling time, calcinations temperature and dwell time. With increasing milling time, calcinations temperature and dwell time, the qualitative concentration of Mg4Nb2O9 phase increased. Pure Mg4Nb2O9 nanopowders with average particle size of 72.5 nm were primary synthesized at 900 °C for 3 h from 60 h powders. The Mg4Nb2O9 ceramics with almost full density and an excellent microwave dielectric properties (ɛr = 12.6, Q × f = 175,810 GHz) were obtained after annealing at 1200 °C from the milled 60 h powders.

Ceramics with the chemical compositions of CaCu3−xSrxTi4O12 (0 ≤ x ≤ 0.4) (CCSTO) were prepared by the conventional solid-state reaction method and the dielectric properties were investigated. It is found that the dielectric loss decreases with increasing x and reaches 0.03 for x = 0.4, meanwhile, the permittivity remains above 3000. Scanning electron microscopy and Energy Dispersive X-ray results indicate the solutions of SrTiO3 and CaTiO3 emerge at grain boundaries. Correspondingly, the impedance spectroscopy analysis confirms that the decrease of dielectric loss is mainly attributed to the increase in the resistivity of the grain boundary. The permittivity and dielectric loss of CCSTO ceramics exhibit very little dc bias dependence (Δɛ′/ɛ′ < 3% up to 0.8 kV/cm) at 10 kHz. These results indicate that CCSTO ceramics have a promising applied prospect with high-permittivity, sufficiently low dielectric loss, and better dc bias voltage stability.

The 100(1 − y) wt%Ba1−xSrxTiO3–100y wt%Mg2TiO4 (BST-MT, 0.45 ≤ x ≤ 0.6, 0.3 ≤ y ≤ 0.7) composite ceramics were fabricated by mixing (Ba,Sr)TiO3 and Mg2TiO4 powders via a conventional ceramic processing technique. The sintering behavior, microstructures, and dielectric properties of composite ceramics were investigated. The dense BST-MT composite ceramics were obtained at a temperature range from 1350 to 1430 °C without forming the impurity phases. By adjusting the relative content of two components and the Ba/Sr ratio in (Ba,Sr)TiO3, an optimum ceramic composite with dielectric constant ∼76.5, loss tangent ∼0.0007 at 10 kHz and 20 °C, dielectric tunability ∼10.2% under a dc electric field of 20 kV cm−1 and good temperature stability of dielectric constant was attained.

Correction for ‘Origin of colossal permittivity in (In1/2Nb1/2)TiO2via broadband dielectric spectroscopy’ by Xiao-gang Zhao et al., Phys. Chem. Chem. Phys., 2015, 17, 23132–23139.

(In1/2Nb1/2)TiO2 (IN-T) ceramics were prepared via a solid-state reaction route. X-ray diffraction (XRD) and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compounds. The results indicated that the sintered ceramics have a single phase of rutile TiO2. Dielectric spectroscopy (frequency range from 20 Hz to 1 MHz and temperature range from 10 K to 270 K) was performed on these ceramics. The IN-T ceramics showed extremely high permittivities of up to ∼103, which can be referred to as colossal permittivity, with relatively low dielectric losses of ∼0.05. Most importantly, detailed impedance data analyses of IN-T demonstrated that electron-pinned defect-dipoles, interfacial polarization and polaron hopping polarization contribute to the colossal permittivity at high temperatures (270 K); however, only the complexes (pinned electron) and polaron hopping polarization are active at low temperatures (below 180 K), which is consistent with UDR analysis.

Retraction of ‘Origin of colossal permittivity in (In1/2Nb1/2)TiO2via broadband dielectric spectroscopy’ by Xiao-gang Zhao et al., Phys. Chem. Chem. Phys., 2015, 17, 23132–23139.