1. Wide Frequency Dependence of Impedance, Electric Modulus and Conductivity of Lead-Free Ba0.5Sr0.5Ti(1-X)InxO3 Ceramics
H.Z. Akbas1, Z. Aydin1, A.Colak1, S. Ustabas1
1: Mustafa Kemal University, Hatay, 31000, TR.
Abstract
Results
Discussions
The frequency dependence of impedance, electric modulus and conductivity of lead-free Ba0.5Sr0.5Ti(1-x)InxO3 (x=0, 4, 8, 10 %) ceramics are investigated over a frequency range 10-2 Hz to 2x107 Hz at room temperature.
An ultrasonic processor with 7 mm titanium probe was used to homogenize the reagents in distilled water for 5 minutes. The water evaporated at 120 ° C and the powders are calcined at 1100 °C in the air atmosphere in the oven.
X-ray diffraction analysis confirmed that all powders are BaSrTiO3 based ceramics and showed that crystal system of powders is cubic.
The ceramic powders were pressed into pellets and sintered at 1400 °C for 4 hours.
The sintered pellet without Indium (In) have many pores on the surface while sintered pellets with In have smooth surface according to scanning electron microscopy (SEM) images.
Complex impedance ( Z’ and Z”), complex electric modulus (M’ and M”) and complex AC conductivity (σ*) were analyzed in a wide frequency range of 10-2 Hz to 2x107 Hz at room temperature.
Z’ and Z” decreased with increasing frequency for each sample.
M’ of ceramics increased with increasing frequency between 10-1 Hz to 103 Hz. M’ of ceramics tended to zero at 10-2 Hz frequency while reached a limit higher frequencies. M” of ceramics has a peak about 20 Hz except Ba0.5Sr0.5TiO3. Each plot of M’ versus M” with different In content has a semicircle that not centered on the real axis.
σ* of samples decreased with increasing In content.
Barium Strontium Titanate (BST) ceramics have been developed for application in a wide variety of fields, such as power devices, capacitors, microwave applications[1,2].
Normally, BST has high dielectric constant and low-loss tangent at room temperature [2]. But it can be converted to electronic and/or ionic conductor when properly doped [3].
Semiconducting BST can be produced by substitution of the tetravalent Ti ions by trivalent In ions.
Complex impedance spectrum gives electrical properties of materials with the larger resistance whereas complex modulus spectrum suggest with smaller capacitance [4].
Relaxation peaks of M” shifts towards the higher frequencies with increasing In content, which hopping mechanism of charge carriers dominates intrinsically[4].
One semi-circle of M’ vs. M” spectrum confirms the single phase of the character, which indicates grain and/or grain boundary contributions of the materials [5].
Figure 1. X-ray diffraction patterns of powders. 0% 4% 8%
10%
Figure 2. Scanning electron microscopy (SEM) images of pellets
Acknowledgements
This work is supported by grant 8980 from Scientific Research Projects Coordination Unit of Mustafa Kemal University (MKU-BAP).
The authors are grateful to MARGEM, Mustafa Kemal University, for helping to collect SEM, XRD, TGA and DSC data.
Figure 3. Reel part of Impedance
Figure 4. Imaginary part of Impedance
Methods
References
BaCO3 , SrCO3 , TiO2 and In2O 3 powders are used analytical grade with purity better than %99.5.
An ultrasonic processor with 7 mm titanium probe was used to homogenize the reagents in distilled water for 5 minutes. The water evaporated at 120 °C and the powders are calcined at 1100 °C in the air atmosphere in the oven.
X-ray diffraction (XRD) with (Rigaku, SmartLab) confirmed that all powders are BaSrTiO 3 based ceramics.
The ceramic powders were pressed into pellets and sintered at 1300 °C for 2 hours.
Scanning electron microscopy (SEM) (JEOL, ) images were used to analyze the morphology of pellets.
Complex impedance measurements were analyzed by dielectric spectrometer (Novocontrol ,BDS41) in a wide frequency range of 10-2 Hz to 2x107 Hz at room temperature.
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Figure 5. Reel part of Electric Modulus
Figure 6. Imaginary part of Electric Modulus
Figure 7. Reel part of Electric Modulus versus . Imaginary part of Electric Modulus
Figure 8. Complex AC conductivity