Confirmation of the second phase transition in CoSiF₆.6H₂O from heat capacity and dielectric constant measurements

Abstract

From heat capacity measurement (using a conduction type calorimeter) a second transition has been observed in CoSiF₆.6H₂O around T_c2 ∼ 200 K along with its first transition at T_c1 ∼ 260K (observed earlier from magnetic susceptibility measurements). Both the transitions are first order in nature. We suggest that the two types of silicon groups attached to the hydrogen bonds (linking [CO(H₂O)]²⁺ and (BF₆)^2-) get ordered at two different temperatures T_c1 and T_c2 (T_c1 > T_c2 ). This is responsible for the two phase transitions in this crystal. The newly observed transition at T_c2 also manifests itself in the anomalous variation of dielectric constants measured at two frequencies (1 kHz and 5 kHz).

Key Words:

• Phase Transition
• CoSiF₆
• 6H₂O
• Specific heat
• Dielectric constant