Eur. Phys. J. B (2012) 85: 235
https://doi.org/10.1140/epjb/e2012-30183-2

Regular Article

Dielectric signature of charge order in lanthanum nickelates

¹ Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
² Department for Resource Strategy, University of Augsburg, 86159 Augsburg, Germany

^a e-mail: peter.lunkenheimer@physik.uni-augsburg.de

Received: 2 March 2012
Received in final form: 27 April 2012
Published online: 5 July 2012

Abstract

Three charge-ordering lanthanum nickelates La_2−xA_xNiO₄, substituted with specific amounts of A = Sr, Ca, and Ba to achieve commensurate charge order, are investigated using broadband dielectric spectroscopy up to GHz frequencies. The transition temperatures of the samples are characterized by additional specific heat and magnetic susceptibility measurements. We find colossal magnitudes of the dielectric constant for all three compounds and strong relaxation features, which partly are of Maxwell-Wagner type arising from electrode polarization. Quite unexpectedly, the temperature-dependent colossal dielectric constants of these materials exhibit distinct anomalies at the charge-order transitions. This phenomenon is ascribed to a variation of intrinsic material properties affecting the formation of depletion layers at the electrode-sample interfaces.