Microstructural and nonohmic properties of ZnO.Pr6O11 CoO polycrystalline system

Abstract

the effective cross-section area of the elements is increased 14 . Several studies describe the dependence of varistor properties on processing conditions of Pr-doped ZnO varistors, especially in the field of grain boundary formation [2][3][4] 13 . It is very important to understand the structure, composition and properties of the boundaries since they have a strong influence on electrical properties. Our purpose is to investigate the microstructure, the current density-electric field (J vs. E) characteristics, and the capacitance-voltage (C-V) characteristics of ZPC varistor systems. Experimental ProcedureThe varistor systems (95-x) mol% ZnO + x mol% Pr 6 O 11 + 5 mol% CoO (x = 0.1, 0.5 and 1.0) were prepared from the mixture of oxide precursors method, all of them being analytical grade oxides: ZnO (Aldrich-99.99%), Pr 6 O 11 (Aldrich-99.9%) and CoO (Riedel-99.9%). The starting materials were attrition-milled in water for 3 hours. Then the dry slurry was calcined at 750 °C in air for 2 hours. The calcined powders were pulverized using agate mortar and pestle and after 2 wt. (%) polyvinyl alcohol (PVA) binder addition, granulated by sieving 200-mesh screen to produce the starting powder. The powder was uniaxially pressed into discs of 12 mm diameter and 1 mm thickness at a pressure of 80 MPa. The pellets were sintered at 1300 and 1350 °C for 2 hours with a heating rate of 5 °C/min followed by furnace cooling. The samples were characterized by X-ray diffraction (XRD, Rigaku, 20-2000), 40 kV and 150 mA from 2θ (20 to 80°), ∆2θ = 0.02°, with Cukα wavelength monocromatized by a graphite crystal. To obtain the Scanning Electron Microscopy (SEM) micrographies (ZEISS ® DSM 940 A) the sintered samples were polished and thermally etched by heating at 100 °C below the IntroductionZnO varistor ceramics are resistor devices manufactured by sintering ZnO powder containing various minor additives 1 . It has been recognized that at least two different classes of additives must be added to the ceramic varistors in order to obtain good nonohmic characteristics 2 . The first class of such additives are varistor-forming oxides (VFO), such as Bi 2 O 3 , Pr 6 O 11 , La 2 O 3 , BaO, V 2 O 5 and glass frits. The second class of additives are 3d transition-metal oxides, which improve significantly the nonohmic characteristics 3 . Zinc oxide ceramics, containing Pr 6 O 11 and CoO, which exhibit current nonohmic characteristics, were first reported by Mukae et al. 4 . In fact, the history of Pr 6 O 11 -based ZnO varistors is similar to the Bi 2 O 3 -based ZnO varistors 5 , but they have not been adequately studied. However, the Pr 6 O 11 -based ZnO varistors don't have volatilization of components 3 and they own a simpler microstructure when compared with Bi 2 O 3 -based varistors, which is an important fact for the stability and degradation phenomena [6][7][8][9] . Most of commercial ZnO varistors are ZnO-Bi 2 O 3 -based varistor ceramics, possessing as major additive Bi 2 O 3 . Although they exhibit excellent varistor perform...

Effect of Pr6O11 Substitution on Structural and Dielectric Properties of BaZrTiO5 Ceramic Materials

“…The maximum size of crystal was appeared in sample P 3 as illustrated in Fig.5. Further increase of Pr 6 O 11 causes a decrease in the crystalline size of the sample P 4 this may be attributed to the presence of some secondary phases of Pr 2 O 3 at the grain boundaries which delays the growth of grains and creates an external pressure on the grains [25]. The effect of increasing temperature on endothermic, weight loss and exothermic reaction were examined by the aid of TGA thermograms method for all the prepared samples, Fig.…”

Nanostructured ZnO Arrays Fabricated via Pulsed Electrodeposition and Coated with Ag Nanoparticles for Ultraviolet Photosensors

“…In accordance with [26] photosensitivity S of 1-D ZnO arrays and Ag/ZnO nanocomposites was calculated as ratio of the photocurrent Ip under UV to dark current Id, which were measured at 1 V. To confirm stable work of test samples multiple "on-off" switching of UV irradiation was used. Similar to [5,8], the measurement of C-U characteristics of 1-D ZnO arrays and Ag/ZnO nanocomposites was performed using a "Measurer L, C, R digital E7-12" at a frequency of 1 MHz and an amplitude of the measurement voltage 0.03 V. The measured C-U characteristics were analyzed as was proposed in [27] and used in [5,8,[28][29]. Fig.…”

Структура и свойства электроосажденных в импульсном режиме наноструктурированных массивов ZnO и нанокомпозитов ZnO/Ag на их основе

“…Для анализа ВФХ применяли мето-дику, предложенную в [18] и использованную в [12,19] при описании электрических свойств и электронных параметров поликристаллических полупроводников и варисторов на основе ZnO. Данная методика исходит из модели возникновения двойных симметричных барьеров Шоттки высотой ϕ в зернограничных областях ZnO.…”

“…Согласно [19], концентрация нескомпенсированной ионизированной донорной примеси N d в зернах ZnO и высота барьера ϕ на границе зерен определялись соответственно из тангенса угла наклона прямолиней-ного отрезка к оси смещающего напряжения U и точки пересечения с осью U продолжения этого отрезка на графике зависимости…”