Previous studies [39] have confirmed that all the interfaces,whether they are grain boundaries or phase boundaries or whetherthey belong to the coherent or incoherent interfaces, can inhibit theheat flow without exception through phonon scattering in thesystem, resulting in remarkable reduction in kL. Moreover, thestudies show that the thermal conductivity depends sensitively onthe interface density (interface area per unit volume) following auniversal curve. In other words, kL reduces gradually with theincreasing interface density. Undoubtedly, the volume fraction ofphase boundaries Fp (as listed in Table 1) increase with theincreasing GNs content for f(GNs)/BiSbTe composites. As shown inFig. 8(c), it is quite clear that kL for f(GNs)/BiSbTe decreases with theincreasing Fp, which is originated from the enhanced phononscattering by the incorporated nanosheets and the phase boundaries. Anomalously, k for the 0.3 vol.% GNs/BiSbTe compositesample is larger than that of the 0.4 vol.% GNs/BiSbTe sample, whichcan be attributed to its much higher kC caused by the increase inelectrical resistivity r.