1. Electric Field Sintering of Undoped Barium Titanate
Noah N. Swygert, Richard Floyd, Elizabeth C. Dickey
Center of Dielectrics and Piezoelectrics, Department of Materials Science and Engineering, North Carolina State University
BaTiO3, a perovskite ferroelectric material has shown to
exhibit exceptionally favorable electronic properties such as
a high dielectric constant as well as low loss characteristics.
Such properties have made BaTiO3 a favorable candidate for
implementation in microelectronic applications such as
capacitors, transducers, and ferroelectric memory.[1] The
perovskite structure gives BaTiO3 the possibility to offset the
crystal structure asymmetrically as the central titanium atom
can be shifted relative to the rest of the surrounding lattice.
Tuning of the dielectric constant can be established through
increasing the displacement via an external force/field.
In conventional sintering processes for BaTiO3, pellets are
often brought up to temperatures of ≥1250-1300 oC. The
predominant problem with such temperatures revolves
around phase transformation where there are possibilities of
having abnormal grain growth due to the formation of a
liquid phase. To lower thermal expenditure in the processing
of BaTiO3, it is possible to sinter green bodies under an
applied electric field for increased kinetic driving force
towards full densification of BaTiO3 pellets.
This study aims to examine the sintering process of undoped bulk barium titanate (BaTiO3) with the ultimate goal to study the effects of an applied electric field on sintering BaTiO3 pellets. BaTiO3 is known for its high dielectric
constant and non-toxic properties compared to its commercially rivaled counterpart lead zirconia titanate (PZT) and is widely used in multi-layer ceramic capacitors (MLCCs). Thus, BaTiO3 has been studied extensively to progress
the microelectronic industry. From previous studies, it is found that the application of an electric field can decrease the temperature required for full densification of sintered pellets. Uniaxially pressed BaTiO3 green bodies was
sintered under conventional sintering temperatures (1250 – 1300 oC) and density measurements were taken for comparison against electric field effect sintering samples. Pellet density measurements were analyzed for the
study. Completion of this study can lead to the further development of changing sintering procedures. Through the completion of this study, industrial processing condition can be remodeled in order to save thermal and energy
expenditure during processing of BaTiO3.
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Density(%)
Sinter Time (hrs)
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NC STATE UNIVERSITY
Future Plans
DilatometerIntroduction
Abstract
References
Discussion
• From the density data, we conclude that temperatures >1200 oC
are required for full densification which agree with current
literature.
• According to Dr. Raj’s work increasing electric field promotes
earlier onset of shrinkage for BaTiO3.
• We attribute the relative similarity of our curves to the current
setup of the dilatometer. More uniform contacts are required
across the surface of the sample.
• We will continue to reproduce Dr. Raj’s published results
• Design a method to ensure uniform contact across the sample
to prevent “hot spots” created by a rough contact.
• Modify the computer program to allow for electric field studies
of pre-densified samples, in order to study the effects of electric
fields on only grain growth.
Figure 2: Setup of sintering under an applied electric field
[1] M’Peko, J. C. et al. J Eur Ceram Soc, 34, 3655-3660 (2014).
[2] Huan, Y. et al. J Am Ceram Soc, 96, 3369-3371 (2013).
LVDT
+ -
Furnace
Computer
Power Supply
The dilatometer was used to measure linear displacement as a function of
temperature using a linear variable differential transformer (LVDT). This
dilatometer was modified to use platinum pads to contact the sample and apply
a voltage using an external power supply.
Figure 3 shows data resulting from preliminary E-field experiments using the
dilatometer setup. Three curves are present; a control under zero voltage, one
under 100 V/cm, and another under 200 V/cm. Our goal is to reproduce the
results from Dr. Rishi Raj’s group, as shown in figure 4, using our custom
dilatometer setup.[1] Their data shows the difference between FAST and Flash
sintering regimes. They are distinguished by the discontinuity in the initial
shrinkage of the sample.
Figure 1: Caliper density curve for conventional sintering
Figure 4: Strain curve as a function of
temperature showing the difference
between FAST and Flash. [1]
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Shrinkage(mm)
Temperature (C)
Control
100V
200V
Figure 3: Displacement as a function of
temperature under an electric field using
the dilatometer.
Acknowledgments
Prof. Elizabeth Dickey
Dr. Matthew Burch
Richard Floyd
Weston Straka