Specific Heat of PbFX (X = Cl, Br, I) at Low Temperature

Abstract

At very low temperature, below 4 K, the specific heat of PbFCI, PbFBr, and PbFT shows a classical behaviour with a T 3 temperature variation. The obtained Debye temperatures follow the Lindemann relation. Between 4 and 35 K, deviations from the T 3 law appear and are explained by means of two Einstein oscillators. These oscillators are linked to the low frequency optical phonons.Au dessous de 4 K, la chaleur specifique de PbFCI, PbFBr et PbFI presente un comportement classiquc de Debye. Les temperatures de Debye observees obeissent a la relation de Lindemann. Entre 4 et 35 K, des deviations a la loi en T 3 apparaissent et sont expliquees a I'aide de deux oscillateurs d'Einstein lies a des phonons optiques de basse frequence.