Charge Order in NaV2O5 studied by EPR

We present angular dependent EPR measurements in NaV2O5 at X-band frequencies in the temperature range 4.2 K < T < 670 K. A detailed analysis in terms of the antisymmetric Dzyaloshinski-Moriya and the anisotropic exchange interactions yields the following scheme of charge order: On decreasing temperature a quarter-filled ladder with strong charge disproportions, existing for T > 100 K, is followed by zig-zag charge-order fluctuations which become long-range and static below T_SP=34 K.