Enhanced electrical transport and ultra low thermal conductivity resulted in a high thermoelectric figure of merit, ZT, of ∼1 and ∼1.15 at ∼680 K in 4 mol% Pb and 2 mol% Bi doped AgSbSe₂, which are 150 and 190% higher compared to that of the pristine sample, respectively. With this excellent thermoelectric performance, p-type AgSbSe₂, constituting earth abundant Se, offers promise to replace traditional metal tellurides containing expensive and scarce Te for mid temperature (350–700 K) thermoelectric applications.

Thermoelectric “waste heat-to-electrical energy” generation is an efficient and attractive option for robust and environmentally friendly renewable energy production. Simultaneous tailoring of interdependent thermoelectric parameters, i.e. electrical conductivity, thermopower and thermal conductivity, to improve the thermoelectric figure of merit is the utmost challenge in this field. Another important aspect is to develop high performance materials based on cheap and earth abundant materials. We have chosen AgSbSe₂, a homologue of AgSbTe₂ containing earth abundant selenium, as a model system for thermoelectric investigation due to its low thermal conductivity and favourable valence band structure. Herein, we show that by integrating different but synergistic concepts: (a) carrier engineering, (b) second phase endotaxial nanostructuring and (c) bond anharmonicity, we can achieve a maximum ZT of ∼1.1 at 635 K in AgSbSe₂–ZnSe (2 mol%), which is significantly higher than that of pristine AgSbSe₂. The above system therefore offers promise to replace traditional metal tellurides for mid-temperature power generation. We demonstrate a design strategy which provides simultaneous enhancement of electrical transport through optimized doping, superior thermopower by the convergence of degenerate valence bands, and glass-like thermal conductivity due to the effective scattering of phonons by nanostructuring, bond anharmonicity and a disordered cation sublattice.

High-resolution electron energy loss spectroscopy (HR-EELS) is utilized to probe the surface spin canting in nanoparticles of two technologically important magnetic materials, i.e. $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$ and $\mathrm{CoF}{\mathrm{e}}_2{\mathrm{O}}_4$ (CFO). A soft experimental technique has been developed that is capable of extracting EELS spectra with single atomic plane resolution recorded in a single frame. The technique yields information at different depths of the nanoparticle from the surface to the core regions with high signal-to-noise ratio and without beam damage. This enables comparing the fine structures between the surface and core regions of the nanoparticles. The results confirm earlier observations of uniformly oriented spin canting structure for CFO and provide additional information regarding atom site-selective spin canting information. In the case of $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$, preferred canting orientation forming core and shell structure is deduced. Unlike earlier reports based on polarized spin-flip neutron scattering measurement, it is possible from the experimental spectra combined with the first principle-based calculations considering noncollinear magnetism to narrow down the canting angles for $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$ ($T_d,O_h$ tilts 40°, 40°) and CFO ($T_d,O_h$ tilts 17°, 17°). In addition, the role of Dzyaloshinskii-Moriya interaction in stabilizing the spin canting at the nanoparticle surface is discussed. The results demonstrate that HR-EELS can be a powerful technique to probe the magnetic structure in nanodimensional systems and has advantages over neutron-based techniques in terms of superior spatial resolution, site-specific information, and ease of sample preparation.