Clathrate BaNi₂P₄: An Interplay of Heat and Charge Transport Due to Strong Host–Guest Interactions

Abstract

Heat and charge transport properties of the metallic unconventional clathrate BaNi2P4, hosting Ba cations in oversized Ni8P16 cages, are investigated. A novel method of single-crystal growth was developed, yielding 2-3 mm sized crystals of BaNi2P4. We also developed a setup to accurately measure thermal conductivity and electrical resistivity of the synthesized single crystals in a wide temperature range avoiding crystal remounting. BaNi2P4 has a metallic temperature dependence of its electrical resistivity (decreasing with decreasing temperature) and manifests an unconventional T2 power law for 50 K < T < 300 K; below 50 K, the power-law exponent increases gradually such that below 10 K the power law is T5, a predicted but extremely rarely experimentally observed dependence for peculiar electron-phonon interactions. Electronic band structure calculations, consistent with measurements of de Haas-van Alphen oscillations, show large band dispersions with significant contributions of Ba orbitals to states near the Fermi level, which is atypical for clathrates. The thermal properties of BaNi2P4 were probed using a combination of variable-temperature single-crystal X-ray diffraction experiments, heat capacity measurements, first-principles phonon dispersion calculations, and inelastic neutron scattering measurements. BaNi2P4 exhibits significant hybridization of the Ba-guest and NiP framework vibrational modes, which may be enhanced via the detected split of the Ba position, which results in strong Ba-framework interactions.

Unprecedented mid-infrared nonlinear optical materials achieved by crystal structure engineering, a case study of (KX)P2S6 (X = Sb, Bi, Ba)

“…The 3.24 Å ionic Ba-S interactions exhibit certain bond strengths as revealed by theory calculations (vide infra). The structural details of K 2 BaP 2 S 6 are shown in Figure 1 e [57] La 2 Ba 6 Cu 16 P 30 (2.071-2.428 Å), [58] BaCu 2 P 4 (2.183 and 2.289 Å), [59] Ba 8 Cu 16 P 30 (2.159-2.299 Å), [60] La 7 Zn 2 P 11 (2.207(7) Å), [61] Ba 2 Cu 3 P 4 (2.236 Å), [62] and La 4 Zn 7 P 10 (2.151(8) Å), [63] etc. The P-S interatomic distances within Ba 2 P 2 S 6 are 2.016-2.025 Å, which are slightly expanded into a wider range of distances to 1.962-2.057 Å and 1.958(17)-2.066(15) Å for KBiP 2 P 6 and K 2 BaP 2 S 6, respectively.…”

“…The [P 2 S 6 ] motif is isotypic to ethane, constructed by a P-P dimer with three sulfur atoms surrounding each P atom. The interatomic P-P bonds for Ba 2 P 2 S 6 , KBiP 2 P 6 and K 2 BaP 2 S 6 are 2.205 A, 2.219 A, and 2.223(4) A, respectively, which are typical for homoatomic P-P bond distances such as BaCu 5 P 3 (2.263 A), 57 La 2 Ba 6 Cu 16 P 30 (2.071-2.428 A), 58 BaCu 2 P 4 (2.183 and 2.289 A), 59 Ba 8 Cu 16 P 30 (2.159-2.299 A), 60 La 7 Zn 2 P 11 (2.207(7) A), 61 Ba 2 Cu 3 P 4 (2.236 A), 62 La 4 Zn 7 P 10 (2.151(8) A), 63 etc. The P-S interatomic distances within Ba 2 P 2 S 6 are 2.016-2.025 A, and are slightly expanded into a wider range of distances to 1.962-2.057 A and 1.958(17)-2.066(15) A for KBiP 2 P 6 and K 2 BaP 2 S 6 , respectively.…”

New Trick for an Old Dog: From Prediction to Properties of “Hidden Clathrates” Ba2Zn5As6 and Ba2Zn5Sb6

“…The C p / T 3 versus T plot exhibits a broad peak centered around 11 K (Ba 2 Zn 5 Sb 6 ) and 16 K (Ba 2 Zn 5 As 6 ). This is referred to as a Boson peak which is typical for cage-like compounds such as clathrates and fullerenes. , The peak maximum temperature is considered to be ∼20% of the Einstein temperature, , thus allowing us to estimate Einstein temperatures as 55 K (Ba 2 Zn 5 Sb 6 ) and 80 K (Ba 2 Zn 5 As 6 ). These values are in the range of Einstein temperatures reported for various conventional and unconventional clathrates .…”

Recent progress in phosphide materials for thermoelectric conversion

“…57 Fortunately, the low thermal conductivity leads to a good peak 93 Further work on BaNi 2 P 4 found a stronger than predicted interaction between Ba and the covalent framework. 94 While these phases are quite metallic, they point to a large underexplored field still in its infancy when compared to Si and Ge based clathrate thermoelectrics with many more new compositions to be discovered.…”