Pd–Al interaction at elevated temperatures: a TEM and SAED study

Epitaxially grown Pd particles partly embedded in amorphous Al₂O₃ were subjected to annealing and reductive treatments in the temperature range 523–873 K to induce a possible Pd–Al interaction. The structural, morphological and compositional changes were monitored by transmission electron microscopy and selected area electron diffraction. Formation of Pd₄Al₃ and PdAl alloys has been observed upon annealing in 1 bar He for 1 h at T > 523 K and upon reduction in 1 bar H₂ for 1 h at T ≥ 523 K, respectively. Both alloys appear to be stable up to 873 K, although Pd₄Al₃ shows beginning decomposition at and above 873 K. The stability under oxidative conditions was found to be very similar, a transformation back into metallic Pd sets in for both compounds at around 573–623 K. In agreement with previous studies on Pd/SiO₂, the formation of an amorphous hydride phase and/or a heavily distorted Pd lattice has been detected after reduction in hydrogen at 523 K.