Pornsuda Bomlai

Electrical, dielectric, and dynamic mechanical properties of conductive carbon black/epoxidized natural rubber composites:

Electrically conductive epoxidized natural rubber filled with conductive carbon black was prepared. The AC conductivity (σAC), dielectric constant (ɛ′), loss factor (tan δ*) and dynamic mechanical properties of the composites were studied. It was found that the epoxide groups in epoxidized natural rubber molecules positively contributed to AC conductivity, dielectric constant, and tan δ* of the composites. Especially, the composite with epoxidized natural rubber containing 50% mol epoxide (epoxidized natural rubber–50) showed better electrical and dynamic mechanical properties than the composites with epoxidized natural rubber–25 or NR. The effects of conductive carbon black loading level on electrical conductivity and dielectric constant of the epoxidized natural rubber–50/conductive carbon black composites was also studied. The percolation threshold was found at very low content of conductive carbon black at volume fraction of 0.07 with the critical exponent value 2.04. Furthermore, the glass transition temperatures of epoxidized natural rubber–50/conductive carbon black composites were higher than those of epoxidized natural rubber–25/conductive carbon black or NR/conductive carbon black composites, and increased with conductive carbon black content.

Structural and Electrical Properties of AgTaO3–modified (Na0.465K0.465Li0.07) NbO3 Lead-Free Ceramics

The (1−x)(Na0.465K0.465Li0.07)NbO3 - xAgTaO3 lead-free ceramics were fabricated by the solid-state reaction process. The densification enhanced with increasing AgTaO3 content, giving maximum relative density of 98% (x = 0.02). Both orthorhombic-tetragonal (T O–T ) and tetragonal-cubic (T C) phase transition temperature decreased gradually with the increasing AgTaO3 content. The ceramic with a composition of x = 0.02 exhibited excellent electrical properties: the dielectric constant (ϵr) = 470, dissipation factor (tan δ) = 0.022, piezoelectric constant d 33 = 160 pC/N, and Curie temperature T C = 432°C. These results clearly showed that the 0.98(Na0.465K0.465Li0.07)NbO3 – 0.02AgTaO3 ceramics are very promising lead-free piezoelectric candidates.

Enhanced dielectric properties of Ba(Ti, Sn)O3 lead-free ceramics by Bi(Zn0.5Ti0.5)O3 substitution

ABSTRACT The (1-x)Ba(Ti, Sn)O3 -xBi(Zn0.5Ti0.5)O3 lead-free ceramics with x = 0, 0.025, 0.05, 0.075 and 0.1 were prepared by the reaction sintering method. The effects of Bi(Zn0.5Ti0.5)O3 substitution on the densification, phase structure, microstructure and electrical properties of Ba(Ti, Sn)O3 ceramics were investigated. The results showed that the highest density of 6.22 ± 0.04 g/cm3 was achieved in x = 0.1 composition. The crystal structure was found to change from tetragonal in x = 0 composition to cubic at x ≥ 0.025. The room-temperature dielectric constant reaching to 39,560 (1 kHz) with low dielectric loss was achieved in ceramic with x = 0.025. The grain size and Curie temperature were significantly decreased when Bi(Zn0.5Ti0.5)O3 content increased. The AC complex impedance spectroscopy technique was also used to obtain the electrical parameters of (1-x)Ba(Ti, Sn)O3 -xBi(Zn0.5Ti0.5)O3 ceramics. As a result, adding Bi(Zn0.5Ti0.5)O3 is an effective way to enhance the densification and dielectric properties of Ba(Ti, Sn)O3 ceramics.

Microstructural and Electrical Properties of Sn-Modified BaTiO3 Lead-Free Ceramics by Two-Step Sintering Method

Ba(Ti0.92Sn0.08)O3 lead-free ceramics were prepared using a two-step sintering (TSS) technique. Varying the first sintering temperature T1 (1400 and 1500°C) and the dwell time t1 (0, 15, and 30 min), we obtained dense ceramics which were then soaked at a constant temperature of 1000°C (T2) for 6 h (t2). The structural and electrical properties were investigated. XRD results indicated that all the ceramics showed a pure perovskite phase with tetragonal symmetry. Density and grain size increased with higher T1 temperatures and increased t1 dwell times. Enhanced electrical properties were achieved by sintering at the optimized T1 sintering temperature and t1 dwelling time. At the lower T1 sintering temperature of 1400°C, the dielectric and piezoelectric properties and the Curie temperature of the ceramics were improved significantly by increasing t1 dwell time. Further, increasing the sintering temperature T1 to 1500°C, excellent properties were obtained at t1 = 15 min which then deteriorated when t1 was increased to 30 min. The electrical properties of the sample sintered under the T1/t1/T2/t2 condition of “1500/15/1000/6” showed the best values. For this sample the piezoelectric coefficient (d33), dielectric permittivity (er), loss factor (tanδ), and Curie temperature (TC) were 490 pC/N, 4385, 0.0272, and 48°C, respectively.

Effects of Ball Milling on the Properties of (Ba 1- x Ca x )(Ti 0.92 Sn 0.08 )O 3 Lead-Free Ceramics

The (Ba1-xCax)(Ti0.92Sn0.08)O3 (x = 0 and 0.02) lead-free ceramics were prepared by using different ball-milling method and time (common ball milling 24 h, high energy ball milling 1 and 3 h). The two-step sintering method was used for sintered the samples. The densification, structure, dielectric and piezoelectric properties of the ceramics were investigated. The results showed that Ca addition could reduce sintering temperature effectively and enhanced densification at lower temperature when using the common ball-milling type. The XRD patterns of (Ba1-xCax) (Ti0.92Sn0.08)O3 ceramics revealed the change in crystal symmetries from tetragonal to cubic phase with increasing Ca content from 0 to 0.02. However, the crystal structure did not change due to the effect of ball-milling method. Ca incorporation caused a decrease of the grain size and Curie temperature. Moreover, the largest grain size was found in the x = 0 ceramics with 24 h-common ball-milling, whereas the small size (< 5 µm) was obtained for the x = 0.02 ceramics. The dielectric and piezoelectric properties were also affected to Ca addition and ball-milling. High piezoelectric coefficient of d33 = 173 pC/N, dielectric constant εr ~ 3200 and dissipation factor tand ~ 0.05 were obtained for the x = 0 sample with high energy ball-milling for 1 h.

Two-Step Sintering, Microstructure and Electrical Properties of (Ba, Ca)(Ti, Zr)O3 Lead-Free Ceramics

In this work, the (Ba1-xCax)(Ti1-yZry)O3 lead-free ceramics were prepared by the two-step sintering method, and effects of Ca and Zr contents on phase structure, densification, microstructure, and electrical properties were investigated. It was found that all samples showed orthorhombic phase. The highest density of 5.84 ± 0.01 g/cm3 was achieved in x = 0.05, y = 0.05 sample. The average grain size, phase transition temperature, dielectric and piezoelectric properties significantly decreased by introducing of the Ca/Zr content. The ceramics with a small amount of Ca and Zr maintain good piezoelectric properties, and a lower dielectric loss. The composition with x = 0.05, y = 0.025 demonstrated optimum electrical properties of d33 ∼211 pC/N, TC ∼ 119 °C, εr ∼ 1788, and tanδ ∼ 0.04.

Phase Structure, Microstructure and Electrical Properties of Lead-Free (1-x) [Na0.515K0.485]0.94Li0.06(Nb0.99Ta0.01)O3 - BiAlO3 Ceramics

Lead-free (1-x)[(Na0.515K0.485)0.94Li0.06(Nb0.99Ta0.01)O3]-xBiAlO3 (NKLNT-BA; x = 0, 0.005, 0.010, 0.015, and 0.020) ceramics were fabricated by a conventional mixed-oxide method. The effects of BiAlO3 addition on the phase structure, microstructure and electrical properties of ceramic were then studied. The result indicated that grain size decreased with increasing of BiAlO3 content. In the composition range studied, the perovskite phase with the coexistence of the orthorhombic and tetragonal phases was identified at approximately x 0.005 by the X-ray diffraction analysis and dielectric spectroscopy, which led to a significant enhancement of the piezoelectric properties. The tetragonality increased with further increasing x. The temperature dependence of dielectric properties showed that the addition of BiAlO3 slightly decreased the ferroelectric tetragonal-paraelectric cubic phase transition temperature (TC), but greatly shifted the polymorphic phase transition from the ferroelectric orthorhombic to the ferroelectric tetragonal phase (TOT) to lower room temperature. The dielectric and piezoelectric properties are enhanced for the composition near the orthorhombic-tetragonal polymorphic phase boundary. The unmodified-(Na0.515K0.485)0.94Li0.06(Nb0.99Ta0.01)O3 ceramics exhibit optimum electrical properties (d33 = 225 pC/N and TC = 418°C).

Sintering, Microstructure and Electrical Properties of MnO2 and CuO-Doped [Na0.515K0.485]0.94Li0.06(Nb0.99Ta0.01)O3 Ceramics

Ceramics with formula (1-x-y)[Na0.515K0.485]0.94Li0.06(Nb0.99Ta0.01)O3 (NKLNT) xMnO2yCuO (when x, y = 0, 0.005 and 0.01) were prepared by a reaction sintering method. The effects of doping level on sinterability and properties of NKLNT ceramics were studied. The results indicated that the co-doping of MnO2 and CuO was effective in promoting the densification of ceramics. Grain growth during secondary recrystallization was also affected, leading to larger grain size with x, y = 0.01 sample. X-ray diffraction data showed that the orthorhombic tetragonal morphotropic phase boundary existed in all the samples. At room temperature, the dielectric properties of NKLNT ceramics were improved by doping of appropriate MnO2 and CuO content. The temperature dependence of dielectric constant showed a decrease slightly in Curie temperature (TC) with increasing MnO2 and CuO content. The composition with x = 0.005, y = 0 exhibited favorable properties for the promising lead-free piezoelectric candidate material.

Phase Structure, Microstructure and Electrical Properties of BiMnO3-Doped (Na0.515K0.485)0.96Li0.04(Nb0.8Ta0.2)O3 Lead-Free Ceramics

1-x)[(Na0.515K0.485)0.96Li0.04(Nb0.8Ta0.2)O3]-xBiMnO3 (x = 0, 0.002, 0.004, 0.006, 0.008 and 0.010) lead-free ceramics were prepared using a conventional mixed-oxide method. The result indicated that the highest density of 4.89 ± 0.01 g/cm3 was found in 0.6 mol% BiMnO3 - doped sample sintered at 1060 C. Grain size decreased with increasing of BiMnO3 content. In the composition range studied, the perovskite phase with the coexistence of the orthorhombic and tetragonal phases was identified at approximately 0 x 0.006 by the X-ray diffraction analysis, which led to a significant enhancement of the piezoelectric properties. The temperature dependence of dielectric properties showed that the addition of BiMnO3 markedly decreased the ferroelectric tetragonal-paraelectric cubic phase transition temperature (TC), and greatly shifted the polymorphic phase transition from the ferroelectric orthorhombic to the ferroelectric tetragonal phase (TOT) to near room temperature. Sample with x = 0.002 exhibited excellent electrical properties: the dielectric constant (εr) = 1228, dissipation factor (tan δ) = 0.0244, piezoelectric constant (d33) = 235 pC/N, and Curie temperature (TC) = 286 °C. These results clearly showed that the 0.998(Na0.515K0.485)0.96Li0.04(Nb0.8Ta0.2)O3 - 0.002BiMnO3 ceramics are very promising lead-free piezoelectric candidates.