The electrical properties of Mn3O4-doped ZnO

doi:10.1016/j.ceramint.2003.12.028

Ceramics International

Volume 30, Issue 7, 2004, Pages 1301-1306

https://doi.org/10.1016/j.ceramint.2003.12.028 Get rights and content

Abstract

Polycrystalline ZnO doped with 1/3 mol% Mn₃O₄ was prepared by the conventional ceramic processing. From J–E characteristics the varistor behavior with nonlinear coefficient, α between 6 and 17 was confirmed in the Mn-doped ZnO sintered at 1000–1300 °C for 1 h in air, but was changed to ohmic behavior in the 1400 °C sintered specimen. In relation to the grain boundary resistivity, three activation energies of 0.37, 0.87 and 0.96 eV were detected from pre-breakdown J–E–T characteristic curves. The barrier height and donor concentration of the Mn-doped ZnO were calculated as about 1.0 V and 2×10¹⁷ cm⁻³ from C–V characteristics, respectively. Similar to commercial ZnO varistors, the deep bulk trap levels in Mn-doped ZnO were estimated as 0.13 and 0.25–0.32 eV by admittance spectroscopy. The varistor behavior of Mn-doped ZnO ceramics supports the formation of double Schottky type barrier in the grain boundary region. It is thought that the release and adsorption of oxygen on ZnO grain boundaries during the redox reaction of Mn ion is responsible for the varistor behavior of Mn-doped ZnO.

Introduction

Polycrystalline ZnO has numerous applications in such diverse areas as facial powders, piezoelectric transducers, varistors, phosphors, and transparent conducting films [1], [2]. It is important to evaluate the defect levels in bulk ZnO especially in the application of ZnO varistors [2]. The deep or shallow trap levels commonly found in bulk ZnO are as interstitial zinc, oxygen vacancy, and impurity induced donor or acceptor levels [1], [2], [3]. It is known that the manganese oxide in ZnO varistors drastically improve the nonlinear J–E characteristics [1]. The equilibrium between di- and trivalent manganese oxides in oxygen atmosphere is expressed by the equation [5]: $4 Mn_{3} O_{4} + O_{2} → 537 ° C 6 Mn_{2} O_{3} → 959 ° C 4 Mn_{3} O_{4} + O_{2}$

Mn₃O₄ doping on ZnO is expected to cause interesting phenomena in relation to the point defect formation in polycrystalline ZnO. In this study, we prepared ZnO doped with 1/3 mol% Mn₃O₄ sintered at 1000–1400 °C and measured its J–E–T, C–V and G–ω–T characteristics. The origin of varistor behavior has been discussed in relation to interfacial and bulk traps.

Section snippets

Experimental procedure

Reagent grade ZnO (99.9%) and Mn₃O₄ (>99.0%) powders were used as sintering materials. ZnO admixed with 1/3 mol% Mn₃O₄ was prepared by ball milling in a polyethylene jar with zirconia balls of 5 mm diameter as milling media in ethanol. The slurry was dried into a cake, and was sieved through a 100 mesh screen to produce granules without binder. Granules were uniaxially pressed into pellets under 20 MPa and then CIPed at 98 MPa. The pellets were placed in an alumina crucible and sintered between

Result and discussion

The room temperature J–E characteristics of Mn-doped ZnO are shown in Fig. 1. All specimens except 1400 °C sintered one show clearly nonlinear J–E characteristics: α of 6.0–17.5; J_L of 0.1–0.4 mA/cm²; ρ of 2.5×10⁶ to 2.5×10⁹ Ω cm. Fig. 2 shows J–E–T characteristics at 300–500 K of Mn-doped ZnO sintered at 1000 °C. The inflection of the curves in the pre-breakdown region appeared above 400 K, which divided the curve into two regions of different slopes (A and B in Fig. 2). From the respective slope of

Conclusion

ZnO doped with 1/3 mol% Mn₃O₄ and sintered at 1000–1300 °C in air showed distinctive varistor behavior with nonlinear coefficient, α between 6 and 17, but was disappeared in the specimen sintered at 1400 °C. Two activation energies of electron conduction in the pre-breakdown region (i.e. grain boundary region) were measured as 0.37 and 0.71–0.96 eV from J–E–T above 400 K. C–V characteristics tell that doping Mn to pure ZnO forms the double Schottky type barrier in the ZnO grain boundary. The barrier

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Varistor ceramics
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The electrical properties of Mn3O4-doped ZnO

Abstract

Introduction

Section snippets

Experimental procedure

Result and discussion

Conclusion

J. Solid State Chem.

Electrical properties of grain boundaries in polycrystalline compound semiconductors

Semicond. Sci. Technol.

Varistor ceramics

J. Am. Ceram. Soc.

The electrical properties of Mn₃O₄-doped ZnO