Abstract
•Heat capacities of the lithium silicides Li12Si7, Li7Si3, Li13Si4, Li22Si5/Li21Si5.•Using three different calorimeters to cover the temperature range from (2 to 873)K.•Sample characterization based on XRD and lithium content determination.•Supply of polynomial heat capacity functions for four temperature intervals.•Calculation of standard entropies and the entropies of formation of the LixSi.
This work presents the heat capacities of the four lithium silicide phases Li12Si7, Li7Si3, Li13Si4, and Li22Si5/Li21Si5 as a function of temperature over the range from (2 to 873)K. The measurements were carried out using three different calorimeters. The heat capacities were determined over the range between (2 and 300)K by a relaxation technique using a Physical Properties Measurement System (PPMS) from Quantum Design, within the range between (283 and 353)K by means of a Micro DSC II (Setaram), and data between (303 and 873)K were measured by using a Sensys DSC from Setaram applying the Cp-by-step method. The experimental data are given with an accuracy of (1 to 2)% above T=20K and up to 8% below 20K. The results of the measurements at low temperatures permit the calculation of additional thermodynamic parameters such as the standard entropy as well as the temperature coefficients of electronic and lattice contributions to the heat capacity. The results represent a significant broadening of the data basis for thermodynamic calculations (e.g. CALPHAD) in the Li+Si system.