Sioma Baltianski

Analysis of impedance spectroscopy data: Finding the best system function

Impedance spectroscopy gains much attention as a non-destructive analysis technique in many areas of materials science and device manufacturing. While it is relatively easy to collect data, the correct analysis or the data interpretation is not a straightforward task. In this paper, a novel analysis technique that provides a simple mean to identify the best system function is shown.A new taxonomy of all the possible circuit models that are based on RC lumped elements is given. The taxonomy divides the various circuit models into groups of increasing complexity. Its order and family, where for RC elements there are four different families, identify each group. A “black box”, rather than a pre-assumed circuit model, represents the sample under test (SUT). The simplest group (order and family) that describes the SUT accurately within the experimental limitations can be found in a single experiment. In some cases, the best circuit model within the group can also be found by investigating the behavior of the SUT under various changes (i.e., temperature, radiation, other environmental conditions, sample construction, etc.).The technique is demonstrated on various circuits with lumped capacitors and resistors. This is done both on actual systems and on synthetic data with artificial noise. A comparison of this method with a standard Cole-Cole identification demonstrates the power of the new approach.

Identification of the Early Stage of Sintering of Nano- BaTiO3 A Comparative Study

The very early stage of nano-BaTiO 3 sintering was monitored using a number of experimental methods. It was found that in situ impedance spectroscopy provides the most sensitive probe to determine the beginning of the sintering process. Dramatic changes in the impedance can be detected in situ on time scales of minutes at temperature as low as 500°C. The mechanisms behind these changes hardly influence the surface area and do not result in shrinkage. A microscopic model of the process that complies with the experimental observations is suggested and discussed. This includes oxygen vacancy formation in the very early low temperature stage, and particle rearrangement at the beginning of the shrinkage stage.

Nb-Doped Barium Titanate: Concentration-Properties Relations

Nb doped barium titanate (BT) experiences unique phenomena over a range of dopant concentrations. One important phenomenon is the resistivity behavior as a function of donor concentration. The role of the grains and the grain boundaries in this system is not fully established yet. There are diverse opinions on this subject, since this system is usually only in partial equilibrium and hence very complex. We examine the system using Impedance Spectroscopy (IS). Two new analysis methods for IS based on evolutionary programming techniques, which are inspired by biological evolution, have been developed in our lab. Those evolutionary programming techniques are called Genetic Programming (GP) and Genetic Algorithm (GA). This is an approach to solve (or in the case of GA suggest solution for) such ill-posed inverse problems. By implementation and improvement of the use of those techniques for analyzing IS results, we believe that the role of the grains and the grain boundaries can be separated and the physical processes occur can be analyzed.© 2008 ASME