Fig. 3: Atomic micro/nanostructural characterization of Pb_0.98Cu_0.042Se (x = 0.02).

a Low-magnification scanning transmission electron microscopy (STEM) image displaying dense Cu-rich nanoprecipitates (denoted by the green arrows). b, c Atomic-resolution STEM images and corresponding atomic model clearly indicating the structure of Cu₂Se along the [10-1] and [0-10] zone axes, respectively. The inset in (c) is the corresponding fast Fourier transform (FFT) image. d, e High-resolution high-angle annular dark-field (HADDF) STEM images of the semicoherent interfaces at the phase boundary between the Cu₂Se nanoprecipitate and PbSe matrix viewed along different zone axes. The phase interfaces and dislocations are marked by dashed lines and yellow symbols respectively. f High-resolution HADDF-STEM image of a typical dislocation. The yellow arrows give a complete Burgers loop of a dislocation, and the estimated Burgers vector (red arrow) is B_D = 1/2[101]. The dislocation is marked by white symbols. The inset image shows the geometric phase analysis (GPA) strain analysis of the entire area in (f). g Illustration of the semicoherent Cu₂Se nanoprecipitates and influence on phonon and electron transport.