Amorphous films in the system AlPO4–TiO2were prepared by an rf‐sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO2content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO2–TiO2glasses with a negative thermal expansion, in which Ti4+ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titaniumK‐band emission spectra were obtained by X‐ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti4+was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO2