TY  - CONF
T1  - AC Conductivity and Permittivity of Conductor-Insulator Relaxor Composites
A1  - Bowen,C.R.
A1  - Almond,D.P.
A1  - Dent,A.C.
A1  - Comyn,T.P.
Y1  - 2007///
KW  - Composite
KW  - Dielectric
KW  - Permittivity
KW  - PMN-PT
KW  - Porous
KW  - Power law
KW  - Relaxor
KW  - Microstructure
SP  - 59
EP  - 59
JF  - EMF-2007 11th European Meeting on Ferroelectricity
T2  - EMF-2007 11th European Meeting on Ferroelectricity
A2  - Zalar,B.
A2  - Malic,B.
A2  - Bobnar,V.
CY  - Ljubljana, Slovenia
PB  - J. Stefan Institute
N2  - Previous work has shown that large networks of randomly positioned resistors (R) and capacitors (C) can be used to simulate the microstructures of heterogeneous materials. The electrical networks exhibit fractional power law frequency dependences of permittivity and ac conductivity, which are remarkably similar to those reported for a wide range of materials. Two main observations were that (i) the power law dependencies of the electrical networks are observed when the ac conductivities of the resistors and capacitors were similar; i.e. at the condition R~2pi.f.C (where f is frequency) and (ii) the network response was related to the resistor and capacitor values by a simple logarithmic mixing rule.
 The logarithmic mixing rule has been used to model the electrical characteristics of two phase conductor insulator composites, such as PZT water and PZT conducting polymer composites. For a two phase material consisting of a conductor of conductivity, S, and an insulator of permittivity E, the power law frequency dependences of permittivity and ac conductivity should be observed when S~2pi.f.E.E0 (equivalent to the condition R~2pi.f.C). 
In this work high permittivity porous PMN PT relaxor ferroelectric materials are examined as a model system. The open porosity within the PMN PT is infiltrated with a conductor (water with S~ 0.1S/m) to create conductor insulator composites. Due to the high permittivity of the PMN PT (>10,000.E0) the power law dependencies are expected to be observed at relatively low frequencies (f<200kHz). A range of porosity fractions are manufactured and tested to examine of the influence of conductor volume fraction on frequency dependent ac conductivity and permittivity and also evaluate the applicability of the logarithmic mixing rule. Both experimental and model predictions will be presented.
SN  - 978-961-6303-93-4
Y2  - 2007/09/03/
M2  - Bled, Slovenia
ER  -