Phase evolution, crystal structure and dielectric behavior of (1 − x)Nd(Zn0.5Ti0.5)O3 + xBi(Zn0.5Ti0.5)O3 compound ceramics

The phase evolution, crystal structure and dielectric properties of (1 − x)Nd(Zn_0.5Ti_0.5)O₃ + xBi(Zn_0.5Ti_0.5)O₃ compound ceramics (0 ≤ x ≤ 1.0, abbreviated as (1 − x)NZT-xBZT hereafter) were investigated. A pure perovskite phase was formed in the composition range of 0 ≤ x ≤ 0.05. The B-site Zn²⁺/Ti⁴⁺ 1:1 long range ordering (LRO) structure was detected by both XRD and Raman spectra in x ≤ 0.05 samples. However, this LRO structure became gradually degraded with an increase in x. The dielectric behaviors of the compound ceramic at various frequencies were investigated and correlated to its chemical composition and crystal structure. A gradually compensated τ_f value was obtained in (1 − x)NZT-xBZT microwave dielectrics at x = 0.03, which was mainly due to the dilution of dielectric constant in terms of Claussius-Mossotti differential equation.     

Phase structure and electrical properties of (0.8 − x) BaTiO3-0.2Bi0.5Na0.5TiO3-xBaZrO3 lead-free piezoceramics

Lead-free piezoelectric ceramics (0.8 − x)BaTiO₃-0.2Bi_0.5Na_0.5TiO₃-xBaZrO₃ (BT-BNT-xBZ, 0 ≤ x ≤ 0.08) doped with 0.3 wt% Li₂CO₃ were prepared by conventional solid-state reaction method. With the Li₂CO₃ doping, all the ceramics can be well sintered at 1170-1210 °C. The phase structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between tetragonal and pseudocubic phases exists at x = 0.03-0.04. The addition of Zr can improve the piezoelectric properties of BT-BNT ceramics. Furthermore, a relaxor behavior is induced and the tetragonal-cubic phase transition shifts towards lower temperatures after the addition of Zr. The ceramics with x = 0.03 possess the optimum electrical properties: d₃₃ = 72 pC/N, k_p = 15.4%, ?_r = 661, P_r = 18.5 μC/cm², E_c = 34.1 kV/cm, T_c = 150 °C.     

Infrared emissivities and microwave absorption properties of perovskite Sm0.5Sr0.5Co1−xFexO3 (0 ≤ x ≤ 0.5)

Sm_0.5Sr_0.5Co_1−xFe_xO₃ (0 ≤ x ≤ 0.5, SSCF) with perovskite-type structure has been successfully prepared by conventional solid-state reaction as a microwave and infrared multi-functional material. The effects of Fe incorporation on the structure, electrical conductivity, infrared emissivity and microwave-absorbing properties were investigated in detail. XRD results have shown that the perovskite structure of SSCF has an orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5, respectively. The incorporation of Fe in SSCF could contribute to the decrease of electrical conductivity, while the infrared emissivities are increased. Moreover, microwave-absorbing properties in the frequency range of 2-18 GHz at room temperature are sensitive to Fe content. The complex permittivity, complex permeability and electromagnetic loss tangent have suddenly a step change at a certain frequency and the step-change frequency position moves slightly to lower frequencies with Fe increased. The optimal reflection loss calculated from the measured permittivity and permeability is 29.33 dB at 7.97 GHz with a thickness of 2.0 mm.     

Study of structural, dielectric and electrical behavior of (1 − x)Ba(Fe0.5Nb0.5)O3-xSrTiO3 ceramics

Polycrystalline samples of BaFe_0.5Nb_0.5O₃ and (1 − x)Ba(Fe_0.5Nb_0.5)O₃-xSrTiO₃ [referred as BFN and BFN-ST respectively] (x = 0.00, 0.15 and 0.20) have been synthesized by a high-temperature solid-state reaction technique. The XRD patterns of the BFN and BFN-ST at room temperature show a monoclinic phase. The microstructure of the ceramics was examined by the scanning electron microscopy (SEM) and shows the polycrystalline nature of the samples with different grain sizes, which are inhomogeneously distributed through the sample surface. Detailed studies of dielectric and impedance properties of the materials in a wide range of frequency (100 Hz-5 MHz) and temperatures (30-270 °C) showed that properties are strongly temperature and frequency dependent. Complex Argand plane plot of ?″ against ?′, usually called Cole-Cole plots is used to check the polydispersive nature of relaxation phenomena in above mentioned compounds. Relaxation phenomena of non-Debye type have been observed in the BFN and BFN-ST ceramics, as confirmed by the Cole-Cole plots.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

Microwave dielectric properties of (1 − x)ZnMoO4-xTiO2 composite ceramics

(1 − x)ZnMoO₄-xTiO₂ (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO₄ phase coexists with the tetragonal rutile TiO₂ phase, and it is easy for silver to react with ZnMoO₄ to form Ag₂Zn₂(MoO₄)₃ phase and hard to react with TiO₂. When the volume fraction of TiO₂ (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO₄-xTiO₂ composite ceramics increases from 8.0 to 25.2, the Q_f value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τ_f value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?_r = 13.9, a Q_f = 40,400 GHz, and a τ_f = +2.0 ppm/°C.     

High-dielectric-constant and low-loss microwave dielectric in the (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 solid solution system

The microwave dielectric properties and microstructures of (1 − x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr_0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr_0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of −4.7 ppm/°C.     

Characterization of sol-gel synthesised lead-free (1 − x)Na0.5Bi0.5TiO3-xBaTiO3-based ceramics

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 − x)Na_0.5Bi_0.5TiO₃-xBaTiO₃ ceramics with x = 0, 0.03, 0.05, 0.07 and 0.1 are investigated. A structural variation according to the system composition was investigated by X-ray diffraction (XRD) analyses. The results revealed that the synthesis temperature for pure perovskite phase powder prepared by the present sol-gel process is much lower (800 °C), and a rhombohedral-tetragonal morphotropic phase boundary (MPB) is found for x = 0.07 composition which showing the highest remanent polarization value and the smallest coercive field. The optimum dielectric and piezoelectric properties were found with the 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃ composition. The piezoelectric constant d₃₃ is 120 pC/N and good polarization behaviour was observed with remanent polarization (P_r) of 12.18 pC/cm², coercive field (E_c) of 2.11 kV/mm, and enhanced dielectric properties ?_r > 1500 at room temperature. The 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃-based ceramic is a promising lead-free piezoelectric candidate for applications in different devices.     

Improving the piezoelectric thermal stability by tailoring phase transition behavior in the new (1 − x)[0.65PbMg1/3Nb2/3O3-0.35PbTiO3]-xBiZn1/2Ti1/2O3 perovskite solid solutions

The phase transition behavior and its effect on thermal stability of the piezoelectric properties of the (1 − x)[0.65PbMg_1/3Nb_2/3O₃-0.35PbTiO₃]-xBiZn_1/2Ti_1/2O₃ ceramics with 0 ≤ x ≤ 0.06 were investigated. The phase transition from the monoclinic to tetragonal phase was determined by the dielectric constant and elastic constant measurements. The temperature independent piezoelectric response with −d₃₁ = 188 pC/N was obtained from 175 to 337 K for the composition with x = 0.02. The enhanced thermal stability of piezoelectric response was achieved by shifting the monoclinic-tetragonal phase transition to the lower temperature.     

Synthesis, structural and microwave dielectric properties of Al2W3−xMoxO12 (x = 0-3) ceramics

Low dielectric ceramics in the Al₂W_3−xMo_xO₁₂ (x = 0-3) system have been prepared through solid state ceramic route. The phase purity of the ceramic compositions has been studied using powder X-ray diffraction (XRD) studies. The microstructure of the sintered ceramics was evaluated by Scanning Electron Microscopy (SEM). The crystal structure of the ceramic compositions as a result of Mo substitution has been studied using Laser Raman spectroscopy. The microwave dielectric properties of the ceramics were studied by Hakki and Coleman post resonator and cavity perturbation techniques. Al₂Mo_xW_3−xO₁₂ (x = 0-3) ceramics exhibited low dielectric constant and relatively high unloaded quality factor. The temperature coefficient of resonant frequency of the compositions is found to be in the range −41 to −72 ppm/°C.     

Structure, dielectric and electric properties of (Ba0.68−xSr0.308Bi0.006Na0.006Mgx)(Ti0.99Sn0.01)O3 ceramics

(Ba_0.68−xSr_0.308Bi_0.006Na_0.006Mg_x)(Ti_0.99Sn_0.01)O₃ ceramics were synthesized by solid-state reaction process. The samples (X ≤ 0.010) are a mixture of cubic (major) and rhombohedral (minor) phases. The rhombohedral phase causes a large dielectric loss in low temperature regions and plays an important role in diffuse phase transition of ceramics. While X > 0.010, the rhombohedral phase decreases and gradually disappears. The dielectric loss of ceramics in the low temperature regions decreases, and the samples change from the diffuse phase transition to the phase transition of second order, and then to of first order. In the temperature range of 270-370 °C, intrinsic conduction dominates conductivity of ceramics.     

Polymorphic phase transition-induced electrical behavior of BiCoO3-modified (K0.48Na0.52)NbO3 lead-free piezoelectric ceramics

(1 − x)(K_0.48Na_0.52)NbO₃-xBiCoO₃ [KNN-xBC] lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. The effects of the BiCoO₃ addition on the phase structure, dielectric, piezoelectric and ferroelectric properties of KNN-xBC ceramics were systematically investigated. The polymorphic phase transition (PPT) from rhombohedral to orthorhombic phase around room temperature was identified in the composition range of 0.01 ≤ x ≤ 0.02, and the improved electrical properties were induced by this PPT. The KNN-0.01BC ceramics near PPT exhibit optimum electrical properties: d₃₃ ∼ 165 pC/N, k_p ∼ 0.40, P_r ∼ 31.0 μC/cm², and E_c ∼ 12.6 kV/cm. These results indicate that the enhanced piezoelectric properties for alkali niobate can be achieved by forming the coexistence of rhombohedral and orthorhombic phases.     

Structure and dielectric characterization of xNd(Mg1/2Ti1/2)O3-(1 − x)Ca0.6La0.8/3TiO3 in the microwave frequency range

The crystal structures, phase compositions and the microwave dielectric properties of the xLa(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.8Sr_0.2TiO₃ composites prepared by the conventional solid state route have been investigated. The formation of solid solution is confirmed by the XRD patterns. Doping with B₂O₃ (0.5 wt.%) can effectively promote the densification and the dielectric properties of xNd(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. It is found that xNd(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics can be sintered at 1375 °C, due to the liquid phase effect of B₂O₃ addition observed by Scanning Electronic Microscopy. At 1375 °C, 0.4Nd(Mg_1/2Ti_1/2)O₃-0.6Ca_0.6La_0.8/3TiO₃ ceramics with 1 wt.% B₂O₃ addition possesses a dielectric constant (?_r) of 49, a Q × f value of 13,000 (at 8 GHz) and a temperature coefficients of resonant frequency (τ_f) of 1 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 20,000 GHz for x = 0.9 is achieved at the sintering temperature 1400 °C.     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting Mg with Ni

The microwave dielectric properties of La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm³, dielectric constant (?_r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τ_f) of −85 ppm/°C were obtained for La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

Relationships between Zr substitution for Ti and microwave dielectric properties in Mg(ZrxTi1−x)O3 ceramics

The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(Zr_xTi_1−x)O₃(MZ_xT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(Zr_xTi_1−x)O₃ ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr⁴⁺ substitution in the B-site could increase density and grain size. An excess of Zr⁴⁺ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZ_xT ceramics. The temperature coefficient of resonant frequency (τ_f) of Mg(Zr_xTi_1−x)O₃ ceramics slightly increased with increasing Zr content, and the variation in τ_f was attributed to the formation of secondary phases.     

Preparation and electrical properties of perovskite ceramics in the system BaBi1−xSbxO3 (0 ≤ x ≤ 0.5)

The effect of the composition on the electrical properties of BaBi_1−xSb_xO₃ (0 ≤ x ≤ 0.5) negative temperature coefficient (NTC) thermistors was studied. Major phases present in the sintered bodies of BaBi_1−xSb_xO₃ (0 < x < 0.5) ceramics were BaBi_0.5Sb_0.5O₃ compounds with a rhombohedral structure and BaBiO₃ compounds with a monoclinal structure. Most pores were located in the grains of BaBiO₃ and BaBi_0.5Sb_0.5O₃ ceramics. It was apparent that the ρ₂₅ and B_25/85 constant of the thermistors increased with increasing Sb content.     

Charge ordering analysis by electrical and dielectric measurements in Ca2−xPrxMnO4 (x = 0-0.2) compounds

Ca_2−xPr_xMnO₄ (0 ≤ x ≤ 0.2) polycrystalline ceramic powders were synthesized by sol-gel method. The X-ray diffraction (XRD) profiles were indexed with a tetragonal and orthorhombic structure for Ca₂MnO₄ and Pr-doped compounds, respectively. Electrical properties were investigated by dc and ac electrical measurements. The dc measurements have revealed an insulating state for all compounds in 80-350 K temperature range. Both dc and ac measurements have highlighted a charge ordering (CO) transition at T_CO = 233 and 245 K for x = 0.175 and 0.2, respectively. The CO state was found to be accompanied by a jump of the hopping activation energy and a rapid rise of both dielectric permittivity and imaginary part of ac electrical impedance.     

Relationship between structure and properties in high-temperature Bi(Al0.5Fe0.5)O3-PbTiO3 piezoelectric ceramics

Ceramic samples of xBi(Al_0.5Fe_0.5)O₃-(1 − x)PbTiO₃ (BAF-PT, x = 0.05-0.5) solid solutions were fabricated using the conventional solid state reaction method. X-ray diffraction analysis revealed that all compositions can form single perovskite phase with tetragonal symmetry. The relationship between the tetragonal lattice parameters, tetragonality c/a, cell volume, and ferro-piezoelectric characterization as a function of x was systematically investigated. The BAF modification can effectively improve the poling condition at a proper BAF content. A combination of piezoelectric constant of d₃₃ (50-60 pC/N), electromechanical planar coupling coefficients of k_p (20.3-22.5%), and high Curie temperature T_c (>478 °C) suggested that BAF-PT could be a good candidate for high-temperature piezoelectric applications.