IMMITTANCE SPECTROSCOPY Models, data fitting, and analysis

IMMITTANCE SPECTROSCOPYModels, data fitting, and analysis

J. Ross MacdonaldIMSPEMAS Workshop

Warsaw 9/2003

MATERIAL/ELECTRODE CHARACTERIZATION WITH IS

• Bulk resistivity and dispersion• Bulk dielectric constant• Mobile charge concentrations• Mobilities and valence numbers• Bulk dissociation and recombination rates• Electrode reaction rate constant• Electrode adsorption rate constant• Other fit-model parameters

IMMITTANCE SPECTROSCOPY

• Impedance Spectroscopy

• Dielectric Spectroscopy

• Data Analysis• CNLS; INVERSION

• LEVM ---- LEVMW V. 8

CNLS-LEVM-LEVMW

• CNLS: Complex nonlinear least squares fitting. Fit complex data to a model whose parts satisfy the

Kronig-Kramers transform relations

• LEVMW: Windows version of LEVM, a free general CNLS fitting and inversion program. Download it and its manual from http://www.physics.unc.edu/~macd/

• LEVMW can accurately fit data to K0, K1, and many other models. It allows temporal response to be calculated from frequency response and vice versa

ELECTRODE EFFECTS AND SLOPES

BULK K0 AND K1 FIT RESULTS

NEARLY CONSTANT LOSS

CONCLUSIONS

• The Moynihan original modulus formalism dispersion model is theoretically and experimentally incorrect and should be replaced by the corrected modulus formalism.

• The corrected modulus formalism is isomorphic to the Scher-Lax microscopic model and leads to virtually independent of temperature and ionic concentration. 1

1/3,C

• The variable-correlation assumption of the OMF and NCM is unsupported by fits of experimental data using the CK1 CMF model.

• The cutoff model is much superior to all coupling models and requires no ad hoc assumptions.

• Nearly-constant-loss behavior is likely to be associated with coupling between vibrating ions and induced dipoles of the bulk material. A microscopic model of the process is needed.

MATERIAL CHARACTERIZATION

• Conduction characterIntrinsically conducting:

a. Completely blocking electrodesb. Partially blocking electrodes

Intrinsically insulating:a. Dielectric: no mobile chargeb. Leaky dielectric: surface or bulk impurity conduction

• Charge characteristicsSupported: strong supporting electrolyte, as in liquidsUnsupported: no supporting electrolyte, as in glasses, solid

electrolytes, semiconductors