Vibrational dynamics of the host framework in Sn clathrates

Abstract

We use nuclear resonance inelastic X-ray scattering (NRIXS), a relatively new, synchrotronbased, isotope-specific technique in combination with a more traditional one, Raman spectroscopy, to probe the vibrational dynamics of the host frameworks in two Zintl clathrates: K 8 Zn 4 Sn 42 (KZS) and Ba 8 Ga 16 Sn 30 (BGS). From the normalized Sn vibrational density of states obtained from NRIXS we calculate the stiffness, a mean force constant of the Sn environment, the resilience, a compact way of expressing the temperature dependence of the Sn mean square displacement, and several thermodynamic properties. The stiffness and the resilience are approximately 7% lower in KZS, reflecting its larger unit cell compared to BGS. We emphasize the complementariness between NRIXS and Raman spectroscopy and establish a series of benchmarks for a more quantitative evaluation of the Raman spectra for the numerous clathrates that are still not suitable for NRIXS studies.

Elastic properties of type-I clathrate K8Zn4Sn42determined by inelastic X-ray scattering

“…In order to identify low-energy optical phonons, we started our investigation by measuring the IXS spectrum at Q = (8.2, 0, 0) (in unit of 2π/a, where a is the lattice constant). Consistent with our earlier Raman and 119 Sn-based nuclear resonance inelastic X-ray scattering (NRIXS) results [38], the IXS spectrum displays a strong feature around 6.1 meV and weaker excitations extending up to about 30 meV (fig. 1(A)).…”

“…The ampoule was evacuated and sealed under vacuum, placed in a computer-controlled furnace, heated to 650 • C at 1 • C/min, kept at this temperature for 1 h, followed by cooling to 200 • C at 0.1 • C/min and to room temperature at 1 • C/min. A single crystal was selected and mounted on the tip of a glass fiber for X-ray diffraction [38] and IXS measurements at room temperature (fig. 1…”

“…Bottom panels: corresponding phonon dispersions; vertical error bars are smaller than the size of the markers. A strong peak in the Raman and NRIXS spectra [38] is marked as a full square (see also fig. 4, right panel).…”

“…KZS crystallizes in the P m 3n space group. It has a relatively large lattice constant (12.052 Å [38]), leading to a small Brillouin zone (a cube with the side = 0.52 Å−1 ). This translates into a q-difference of only 0.026 Å−1 between two consecutive experimental points (Δξ = 0.05 reciprocal lattice units, r.l.u.)…”

Experimental observation of electron-phonon coupling enhancement in Sn nanowires caused by phonon confinement effects

“…Measurements were performed at sector 30 of the Advanced Photon Source (APS). Details of the experimental set up are reported elsewhere [38]. The measured spectra consist of the photon count rate as a function of the energy difference between the incident photon and the Mössbauer nuclear transition in 119 Sn.…”