DC conductivity of Fe2O3–Bi2O3–B2O3 glasses

doi:10.1016/S0254-0584(98)00281-8

Materials Chemistry and Physics

Volume 58, Issue 3, 15 April 1999, Pages 243-248

https://doi.org/10.1016/S0254-0584(98)00281-8 Get rights and content

Abstract

Fe₂O₃–Bi₂O₃–B₂O₃ system of glasses were prepared by a press-quenching method from glass melts, and their dc conductivities (σ) were determined in the temperature range 373–573 K. The glass formation region was found to be: Fe₂O₃ = 0–40 mol%, Bi₂O₃ = 0–100 mol%, and B₂O₃ = 0–100 mol%. The negative values of Seebeck coefficient showed these glasses to be n-type semiconductors. For temperatures from 373 to 573 K, the dc conductivity increased from 10⁻⁸ to 10⁻⁵ S cm⁻¹ with increasing Fe₂O₃ content. Bi₂O₃ acted as a reducing agent for redox reaction during glass synthesis and effected the conductivity. Different values of the activation energy for two-temperature regions were interpreted to be due to the formation of non-bridging oxygen ion in the glass network, or the variation of dielectric constant probably owing to a phase separation. Electrical conduction of the glasses was confirmed to be non-adiabatic small polaron hopping. The conductivity was primarily determined by carrier mobility.

Introduction

Extensive studies have been carried out on semiconducting oxide glasses containing transition metal ions owing to interests in their conduction mechanism and glass structure 1, 2, 3, 4, 5, 6, 7, 8. The mechanism of electrical conduction on semiconducting oxide glasses has generally been understood in the light of the small polaron hopping (SPH) model [3]. In 1989, Shimakawa [9]proposed a transport model based on multiphonon tunneling with weak electron–lattice coupling, which could explain the mechanism for dc conductivities for binary phosphate and tellurite glasses.

We have reported dc conductivity of the Fe₂O₃-containing glasses in the system Fe₂O₃–Sb₂O₃–TeO₂ [10], Fe₂O₃–SrO–TeO₂ [11], Fe₂O₃–MoO₃–TeO₂ [12], and Fe₂O₃–PbO–Bi₂O₃ [13]. The conduction of glasses in these systems was confirmed to be due to electronic hopping of small polarons. Fe₂O₃–Sb₂O₃–TeO₂ glasses also exhibited paramagnetic behavior [14]. If Fe ion containing glasses with a high electrical conductivity can be obtained at room temperature, then these glasses may find useful applications as sensors in magneto-resistance effect.

It is noteworthy that Fe₂O₃ is not a glass network former; this makes it relatively difficult to prepare glasses containing highly Fe³⁺ ions, because the maximum range for glass formation is with Fe₂O₃ = 15–20 mol% [8]. In our endeavour to obtain Fe ion containing glasses of high conductivity, we were interested in the Fe₂O₃–Bi₂O₃–B₂O₃ system because its glass formation region and a maximum range of Fe₂O₃ content were expected to expand further, considering that B₂O₃ is a good glass network former and Bi₂O₃-containing glasses could be formed without other conventional network formers by rapid quenching [13]. In this study, Fe₂O₃–Bi₂O₃–B₂O₃ glasses were prepared by the press quenching technique, and the dc conductivity (σ) was determined to elucidate the conduction mechanism.

Section snippets

Experimental procedure

Using reagent grade Fe₂O₃(98%), Bi₂O₃(99.9%) and B₂O₃(90%), a glass batch (5 g) was prepared by melting in an electric furnace in air at 1423 K for 1 h. The melt was then press-quenched between two copper blocks. Glass samples about 1 mm thick with an area 4 cm² were prepared. The glass formation region was determined by X-ray diffraction. The differential thermal analysis (DTA) measurements were made using a Rigaku differential scanning calorimeter with data acquisition system, Model TAS-100, with

Glass formation region

The glass formation region of the Fe₂O₃–Bi₂O₃–B₂O₃ is illustrated in Fig. 1 indicating a compositional range for glass formation: 0 ≤ Fe₂O₃ ≤ 40 mol%, 0 ≤ Bi₂O₃ ≤ 100 mol% and 0 ≤ B₂O₃ ≤ 100 mol%. This compositional range was found to be larger than those in our previous studies on Fe₂O₃ glasses 10, 11, 12, 13.

From DTA measurements, the glass transition temperature (T_g) of the Fe₂O₃ : Bi₂O₃ : B₂O₃ = 40 : 40 : 20 mol% glass, was obtained to be 773 K. This value is larger than those of tellurite glasses (T_g = 498–548 K) [8],

Conclusions

Glasses in the system Fe₂O₃–Bi₂O₃–B₂O₃ were prepared using the press-quenching technique from the glass melts and the dc conductivity was investigated. The glass formation region was determined to be in the range of composition as 0 ≤ Fe₂O₃ ≤ 40 mol%, 0 ≤ Bi₂O₃ ≤ 100 mol% and 0 ≤ B₂O₃ ≤ 100 mol%. The glasses were n-type semiconductors.

The dc conductivity ranged from 10⁻⁸ to 10⁻⁵ S cm⁻¹ at temperatures between 373 and 573 K. The conductivity increased with increasing Fe₂O₃ content. Different values of the

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DC conductivity of Fe2O3–Bi2O3–B2O3 glasses

Abstract

Introduction

Section snippets

Experimental procedure

Glass formation region

Conclusions

J. Non-Cryst. Solids

Mater. Chem. Phys.

Mater. Lett.

J. Non-Cryst. Solids

Solid State Commun.

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Ann. Phys.

J. Non-Cryst. Solids

J. Non-Cryst. Solids

Adv. Phys.

Adv. Phys.

Phys. Rev. B

Yogyo-Kyokai-Shi

Seramikkusu Ronbunshi

DC conductivity of Fe₂O₃–Bi₂O₃–B₂O₃ glasses