Molten salt synthesis and properties of three new solid-state ternary bismuth chalcogenides, .beta.-CsBiS2, .gamma.-CsBiS2, and K2Bi8Se13

LiBi3S5—A lithium bismuth sulfide with strong cation disorder

“…For the 7 Li-NMR measurements under static, i.e., non-rotating conditions, the LiBi 3 S 5 powder prepared was fire-sealed under vacuum in DURAN ® glass ampoules (ca. 4 cm in length and 0.5 cm in diameter) to permanently protect the sulfide from any moisture or air.…”

“…4 cm in length and 0.5 cm in diameter) to permanently protect the sulfide from any moisture or air. 7 Li-NMR measurements were performed using a "Bruker Avance III" spectrometer, which was connected to a shimmed cryomagnet with a nominal external magnetic field of B 0 = 7.04 T, which corresponds to a 7 Li resonance frequency of ω 0 /2π = 116.4 MHz. A ceramic high-temperature NMR probe (Bruker BioSpin) was employed that allows π/2 pulse lengths of ca.…”

“…The temperature in the sample chamber (223 to 573 K) was adjusted via a "Eurotherm" controller and a stream of freshly evaporated dinitrogen. 7 Li-NMR spectra and 7 Li spin-lattice relaxation (SLR) rates (1/T 1 = R 1 ) in the laboratory frame of reference were recorded with the wellknown saturation recovery pulse sequence. In our case, this sequence consists of ten π/2 pulses destroying any longitudinal magnetization M followed by an evolution period allowing for the recovery of M(t d ): 10 × π/2-t d -π/2-acquisition (acq).…”

“…In addition, we used spin-lock NMR relaxometry to probe slower ion dynamics. 7 Li SLR rates in the so-called rotating frame of reference (1/T 1ρ = R 1ρ ) were recorded with the following pulse sequence: π/2 X′ -spin-locking pulse (t lock )-acq. The first pulse flips the equilibrium magnetization M into the (xy)′-plane; the spin-lock pulse, directly following the pulse to prepare the spin-system, is used to hold the transversal component of M. During the locking pulse, which is generated via the Β 1 field characterized by ω 1 /2π in the kilohertz range, M has to adopt a new equilibrium value that is much smaller than that corresponding to B 0 .…”

“…This class of compounds has proven to be remarkably large and has contributed many complex compositions and structures favorable for high thermoelectric performance [3], e.g., K 2.5 Bi 8.5 Se 14 [4], β-K 2 Bi 8 Se 13 [4], A 2 Bi 8 Se 13 (A = Rb, Cs) [5], and CsBi 4 Te 6 [6]. In comparison to selenides and tellurides, most of the alkali-metal bismuth sulfides exhibit wide energy band gaps and strong ionic interactions between the alkali-metal ions and the [Bi x S y ] z-framework, e.g., in β-and γ-CsBiS 2 [7], γ-RbBi 3 S 5 [8], and KBi 3 S 5 [9]. Because of these characteristics, further compounds of this class are sought after.…”