Specific heat and the cooperative Jahn-Teller effect in KDy(WO4)(2)

The specific heat of KDy(WO4)(2) has been measured over the wide temperatur e range from 3.5 K to 200 K. Only one anomaly, indicating the phase transit ion driven by the cooperative Jahn-Teller effect, has been found, at T-JT = 6.4 K. The phonon specific heat has been estimated and subtracted from the heat capacity measured. The Schottky anomaly originating from the populati on of the lowest two doublets of the dysprosium ions, and the lambda-anomal y connected with the Jahn-Teller phase transition have been described theor etically using the molecular-held approximation. Satisfactory agreement bet ween experimental points and theoretical dependences calculated using the m aterial parameters known from the literature was obtained.