Thermal Expansion of Ti₅Si₃ with Ge, B, C, N, or O Additions

The crystallographic thermal expansion coefficients of Ti₅Si₃ from 20 to 1000 °C as a function of B, C, N, O, or Ge content were measured by high-temperature x-ray diffraction using synchrotron sources at Cornell University (Cornell High Energy Synchrotron Source; CHESS) and Argonne National Laboratory (Advanced Photon Source; APS). Whereas the ratio of the thermal expansion coefficients along the c and a axes was approximately 3 for pure Ti₅Si₃, this ratio decreased to about 2 when B, C, or N atoms were added. Additions of O and Ge were less efficient at reducing this thermal expansion anisotropy. The extent by which the thermal expansion was changed when B, C, N, or O atoms were added to Ti₅Si₃ correlated with their expected effect on bonding in Ti₅Si₃.