Origin of apparent colossal dielectric constants

Experimental evidence is provided that colossal dielectric constants ε^'>~1000, sometimes reported to exist in a broad temperature range, can often be explained by Maxwell-Wagner-type contributions of depletion layers at the interface between sample and contacts or at grain boundaries. We demonstrate this on a variety of different materials. We speculate that the largest intrinsic dielectric constant observed so far in nonferroelectric materials is of order 10².