From Lattice Distortion to Phonon Scattering: Understanding the Reduced Thermal Conductivity of Mono‐Doped La 2 Zr 2 O 7 Matiullah Khan, Zeng Yi
ABSTRACT
Introducing lattice strain and chemical disorder by incorporating foreign atoms in zirconates is an effective tool for controlling the phonon transmission. Mono‐isovalent Ho, Er, and Nd substitution at La sites effectively suppresses the conductivity by intensified phonon scattering coming from the local strain field. X‐ray diffraction analysis confirms the presence of Ho 2 O 3 in Ho‐La 2 Zr 2 O 7 (HLZO) and Er 2 O 3 in Er‐La 2 Zr 2 O 7 (ELZO). Moreover, the Nd‐La 2 Zr 2 O 7 (NLZO) provides the La 2 Zr 2 O 7 (LZO) phase without any secondary phase. Highly agglomerated, irregularly shaped fine particles are observed through a scanning electron microscope. In energy dispersive X‐ray spectroscopy, the peaks related to Ho, Er, and Nd are found. Pure LZO exhibits the lowest, and HLZO demonstrates the highest thermal expansion coefficient values among the synthesized samples. The HLZO is composed of fine particles and abundant grain boundaries that, in addition to local strain fields and point defects, influence the thermal transport. The LZO possesses the highest, and HLZO provides the lowest thermal conductivity values in the entire range of investigated temperatures. The HLZO with a highly disordered yet structurally stable pyrochlore framework provides intense phonon scattering through the combined effect of mass fluctuation, local strain fields, high grain boundary density, and suitable arrangement of point defects, providing an appropriate material for high‐temperature applications.