Dielectric behavior and charge ordering inNaV2O5

We report the dielectric function of ${\mathrm{NaV}}_2{\mathrm{O}}_5$ single crystals in the gigahertz range as a function of the temperature. Well-defined dielectric anomalies are observed along all directions at the phase transition around 33 K on both the real and imaginary parts. Although the most anomalous behavior is seen along the two-leg ladders $(b$ axis), the largest anomaly is obtained along the rungs $(a$ axis). These results are discussed in relation with the zigzag structure of a charge ordering model that has been suggested to explain the phase transition and the physical properties below 33 K.