Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn_0.9Cu _x Mn_2.1-x O₄ (0.1?≤?x?≤?0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn_0.9Cu _x Mn_2.1-x O_\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn³⁺ ions at the B sites. Cu2p_3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn_0.9Cu _x Mn_2.1-x O₄ varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.     

Preparation and characterization of negative temperature coefficient (Ni,Mn)<Subscript>3</Subscript>O<Subscript>4</Subscript>–La(Mn,Ni)O<Subscript>3</Subscript> composite

The composites made of spinel-structured (Ni,Mn)₃O₄ and perovskite-structured La(Mn,Ni)O₃ were investigated for potential application as negative temperature coefficient (NTC) thermistor. The composites were prepared using the standard ceramic route. The electrical resistivity of the composite at 25°C was found to decrease by one to two orders of magnitude depending the amount of the low-resistivity perovskite phase, while the thermal constant determining the temperature sensitivity of the NTC thermistor was still reasonably large in the range of 4,000 to 3,000 K, and the resistivity drift after annealing at 150°C for 1,000 h in air was relatively small (∼1.2%). The general effective media model was adopted to fit the electrical resistivity data of the composites, giving a value of 0.37 for the percolation volume fraction of the perovskite phase. This work demonstrates that it is possible to tune the electrical resistivity and thermal constant of the spinel-structured oxide through making composite with low-resistivity perovskite-structured oxide.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

Piezoelectric characteristics of low temperature sintering Pb(Ni1/3Nb2/3)O3–Pb(Zr1/2Ti1/2)O3 ceramics as a function of Pb(Mn1/3Sb2/3)O3 substitution

In this study, in order to develop the composition ceramics for multilayer ceramic for ultrasonic nozzle and ultrasonic actuator application, Pb(Mn_1/3Sb_2/3)O₃ (abbreviated as PMS) substituted Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (abbreviated as PNN-PZT) ceramics were fabricated using two-stage calcinations method and Li₂CO₃, Na₂CO₃ and ZnO as sintering aids, and their piezoelectric and dielectric characteristics were investigated. With the increase of the amount of PMS substitution, electromechanical coupling factor (k _p), and mechanical quality factor (Q _m) of specimens showed the maximum value at 3 mol% substituted specimen while dielectric constant (? _r) was decreased. At the sintering temperature of 900 °C, the density, ? _r, k _p, and Q _m of 3 mol% PMS substituted PNN-PZT composition ceramics showed the optimal values of 7.92 [g/cm³], 959, 0.584, and 1003, respectively, for low loss multilayer piezoelectric actuator application.     

Piezoelectric properties of MnO2 doped low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr0.50Ti0.50)O3 ceramics

In this study, in order to develop the composition ceramics for low loss and low temperature sintering multilayer piezoelectric actuator, Pb(Mn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.50Ti_0.50)O₃ (abbreviated as PMN-PNN-PZT) ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated according to the amount of MnO₂ addition. At the 0.2 wt% MnO₂ doped specimen sintered at 900 °C, density and mechanical quality factor (Q _m) showed the maximum values of 7.81[g/cm³]and 1186, respectively. And also, at 0.1 wt% MnO₂ doped specimen, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) of specimen showed the maximum values of 0.608 and 377[pC/N], respectively. Dielectric constant (? _r) slightly decreased with increasing MnO₂. Taking into consideration the density of 7.81[g/cm³], electromechanical coupling factor (k _p)of 0.597 the mechanical quality factor (Q _m) of 1,186, and piezoelectric constant (d ₃₃) of 356[pC/N], it could be concluded that 0.2 wt% MnO₂ doped composition ceramics sintered at 900 °C was best for low loss and low temperature sintering multilayer piezoelectric actuator application.     

Synthesis, Physicochemical Characterization and Ionic Conductivity of LaGa0.4Mg0.2M0.4O3−δ (M = Cr, Mn, Fe, Co)

Partial electronic and ionic conductivities, crystal structure, thermal expansion and infrared absorption spectra of the perovskite-type series, LaGa_0.40Mg_0.20M_0.40O_3– (M = Cr, Mn, Fe, and Co), have been studied. The rhombohedral distortion of the perovskite lattice decreases and the unit cell volume increases in the sequence Co < Cr < Mn < Fe. The p-type electronic conduction increases with atomic number of the transition metal cation; the activation energy varies in air from 15.9 to 32.1 kJ/mol. The oxygen ionic conductivity of the M-doped phases at temperatures below 1200 K is significantly lower than that of LaGa(Mg)O₃. The highest ionic conductivity was found for the Fe- and Co-containing phases. The ion transference numbers of La(Ga,Mg,M)O_3– at 970–1270 K were determined to vary in a wide range, from 2 × 10^–5 to 3 × 10^–2. Thermal expansion coefficients, calculated from the dilatometric data collected in the temperature range 300–1100 K, lie in the range (7.2–15.5) × 10^–6 K^–1.     

Piezoelectric and dielectric properties of low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr0.48Ti0.52)O3 ceramics with variation of sintering time

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.48Ti_0.52)O₃ (abbreviated as PMN–PZN–PZT) ceramics containing Li₂CO₃, Bi₂O₃ and CuO as sintering aids were fabricated using two-stage calcinations method in order to develop low temperature sintering ceramics for multilayer piezoelectric actuators. Their dielectric and piezoelectric properties were investigated according to the variation of sintering time. All the specimens sintered at 930°C for 60~150 min showed tetragonal phases without secondary phases. Electromechanical coupling factor (kp), dielectric constant (ε _r) and piezoelectric constant (d ₃₃) increased with the increase of the sintering time. The mechanical quality factor (Qm) exhibited maximum of 1,815 with the increase of sintering time for 120 min and then slightly decreased. At the sintering temperature of 930°C and the sintering time of 120 min, the optimal values such as the density of 7.69 g/cm³, kp of 0.516, ε _r of 1158, Qm of 1815, and d ₃₃ of 287 pC/N were found for multilayer piezoelectric actuators.     

Piezoelectric and dielectric characteristics of low-temperature-sintering Pb(Mg1/2W1/2)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics according to the amount of PNN substitution

In this study, in order to develop low-temperature-sintering ceramics for multilayer piezoelectric actuator, Pb(Mg_1/2W_1/2)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (abbreviated as PMW–PNN–PZT) ceramics were fabricated using Li₂CO₃ and CaCO₃ as sintering aids and their dielectric and piezoelectric properties were investigated with the amount of Pb(Ni_1/3Nb_2/3)O₃ (abbreviated as PNN) substitution. PMW–PNN–PZT composition ceramics could be sintered up to 870°C by adding sintering aids. At the sintering temperature of 900°C, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) and Curie temperature (Tc) in the composition ceramics with 9 ;mol% PNN substitution showed the optimal value of 0.64 517 ;pC/N and 317°C, respectively for multilayer actuator application.     

Effect of Temperature on the Elastic and Anelastic Behaviour of Magneto-Ferroelectric Composites Ba0.8Pb0.2TiO3 + Ni0.93Co0.02Mn0.05Fe1.95O4-δ in the Ferroelectric Rich Region

Composites with composition xBa_0.8Pb_0.2TiO₃+ (1 –x) Ni_0.93Co_0.02Mn_0.05Fe_1.95O_4- in which x varies as 1.0, 0.9, 0.7 and 0.5 in molar percent have been prepared by the conventional ceramic double sintering process. The presence of the two phases has been confirmed by X-ray diffraction. These composites were prepared for their use as magnetoferrolectric devices. Variation of longitudinal modulus (L) and internal friction loss (Q ^–1) of these samples with temperature at 142 kHz has been studied in the wide temperature range 300 to 630 K. The elastic behaviour (L) showed a break at the ferroelectric Curie temperature (498 K) in the case of pure ferroelectric material (Ba_0.8Pb_0.2TiO₃). This break shifted to lower temperature side as the ferrite component increases in the composite. The temperature variation of internal friction loss (Q ^–1) showed a corresponding stress induced relaxation peak at the ferroelectric-non-ferroelectric phase transition. This behaviour is explained in the light of structural phase transition.