The onset of copper-ion mobility and the electronic transition in the kesterite Cu₂ZnGeSe₄

Abstract

Powder neutron diffraction reveals that anomalies in electrical-transport properties of Cu2ZnGeSe4 are associated with disordering of copper and zinc cations, which is accompanied by a partial melting of the copper-ion sub-lattice.

Structural, elastic, electronic, optical and anisotropy properties of newly quaternary Tl2HgGeSe4 via DFPT predictions associated to XPES and RS experiments

“… 1 belongs to an interesting family of chalgogenides crystallizing in orthorhombic ( Cmc 2 1 and Pmn 2 1 ) and tetragonal ( I and I 2m) space groups with a common formula A 2 B II D IV Q 4 (A stands for Cu/Ag, B II is referred to Zn/Cd/Hg, D IV serves for Si/Ge/Sn, whereas Q is S/Se/Te) that are of tremendous attention over recent decades from theoretical and technological viewpoints because of a number of practical advantages. Among them are p-type electrical conductivity, energy band gaps being in the range of 1.0–1.6 eV, high values of conversion power and absorption coefficients over 10 4 cm –1 2 – 6 that make these compounds to be indispensable photovoltaic absorbers for novel technologies of thin-film production for solar-cells 7 , 8 , photocatalysts of different conversion reactions 9 , upcoming thermoelectric and hole transport semiconductors 10 , 11 , prospective materials for nonlinear optical (NLO) applications 12 . The tremendous challenge for scientists and engineers over recent decade is to tune the physicochemical properties of the A 2 B II D IV Q 4 chalcogenides to gain unambiguous technological values by chemical alloying, formation of point defects and secondary/metastable phases, preparing solid-solutions 13 , 14 , changing crystal dimensions to nanoscales, etc.…”

The impact of a magnetic ion on the thermoelectric properties of copper-rich quaternary selenides

“…Similarly, annealing of kesterite Cu 2 ZnSnSe 4 thin films below the temperature of the order-disorder phase transition, increases the band gap by 110 meV when compared to that of the fully disordered material [37,38]. The order-disorder phase transition in kesterite-type phases is accompanied by a marked anomaly in ρ(T) and by a weak feature in DSC data [39]. Moreover, DSC data for Cu 2 FeGeS 4 also shows a weak feature between 520 K and 580 K, of unknown origin [40].…”

“…Similar anomalies have been observed previously by Zeier et al [42] in the copper rich samples, Cu 2+x Zn 1−x SnSe 4 , and DSC also reveals an exothermic effect at around 450 K. It has been suggested [42] that this anomaly in electrical transport properties is associated with a semiconductor to metal transition on heating. However, the recent powder neutron diffraction work of Mangelis et al [39] reveals that the anomalies in the electron-transport properties coincide with structural changes involving a second-order phase transition. In particular, disordering of Cu and Zn cations from an initially partially ordered arrangement to a fully disordered state, is accompanied by partial melting of the copper sub-lattice, resulting in delocalization of copper cations at the 2c and 2d positions occupied by Cu and Zn, and at the 2a site occupied exclusively by Cu.…”

Structure Evolution and Bonding Inhomogeneity toward High Thermoelectric Performance in Cu2CoSnS4–xSex Materials

“…The DSC curve of pure sulfide shows an endothermic peak near 586 K which may indicate possible polymorphic phase transition, as was also reported for some other quaternary diamond-like compounds. 57,58 With the increase of x in Cu 2 CoSnS 4−x Se x samples, this effect is almost not visible or even absent on DSC curves.…”