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Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl 2 ( Pnma ), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSe 2 Cl 4 octahedra. The electronic structure of CuBiSeCl 2 is investigated computationally, which indicates highly anisotropic charge carrier effective masses, and by experimental verification using X-ray photoelectron spectroscopy, which reveals a valence band dominated by Cu orbitals. The band gap is measured to be 1.33(2) eV, a suitable value for solar absorption applications. The electronic and thermal properties, including resistivity, Seebeck coefficient, thermal conductivity, and heat capacity, are also measured, and it is found that CuBiSeCl 2 exhibits a low room temperature thermal conductivity of 0.27(4) W K -1 m -1 , realized through modifications to the phonon landscape through increased bonding anisotropy., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

One of the great advantages of organic-inorganic metal halides is that their structures and properties are highly tuneable and this is important when optimizing materials for photovoltaics or other optoelectronic devices. One of the most common and effective ways of tuning the electronic structure is through anion substitution. Here, we report the inclusion of bromine into the layered perovskite [H 3 N(CH 2 ) 6 NH 3 ]PbBr 4 to form [H 3 N(CH 2 ) 6 NH 3 ]PbBr 4 ·Br 2 , which contains molecular bromine (Br 2 ) intercalated between the layers of corner-sharing PbBr 6 octahedra. Bromine intercalation in [H 3 N(CH 2 ) 6 NH 3 ]PbBr 4 ·Br 2 results in a decrease in the band gap of 0.85 eV and induces a structural transition from a Ruddlesden-Popper-like to Dion-Jacobson-like phase, while also changing the conformation of the amine. Electronic structure calculations show that Br 2 intercalation is accompanied by the formation of a new band in the electronic structure and a significant decrease in the effective masses of around two orders of magnitude. This is backed up by our resistivity measurements that show that [H 3 N(CH 2 ) 6 NH 3 ]PbBr 4 ·Br 2 has a resistivity value of one order of magnitude lower than [H 3 N(CH 2 ) 6 NH 3 ]PbBr 4 , suggesting that bromine inclusion significantly increases the mobility and/or carrier concentration in the material. This work highlights the possibility of using molecular inclusion as an alternative tool to tune the electronic properties of layered organic-inorganic perovskites, while also being the first example of molecular bromine inclusion in a layered lead halide perovskite. By using a combination of crystallography and computation, we show that the key to this manipulation of the electronic structure is the formation of halogen bonds between the Br 2 and Br in the [PbBr 4 ] ∞ layers, which is likely to have important effects in a range of organic-inorganic metal halides., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

A tetragonal argyrodite with >7 mobile cations, Li 7 Zn 0.5 SiS 6 , is experimentally realized for the first time through solid state synthesis and exploration of the Li-Zn-Si-S phase diagram. The crystal structure of Li 7 Zn 0.5 SiS 6 was solved ab initio from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li 7 Zn 0.5 SiS 6 adopts a tetragonal I 4 structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1 K to a higher symmetry disordered F 43 m structure more typical of Li-containing argyrodites. Simultaneous occupation of four types of Li site (T5, T5a, T2, T4) at high temperature and five types of Li site (T5, T2, T4, T1, and a new trigonal planar T2a position) at room temperature is observed. This combination of sites forms interconnected Li pathways driven by the incorporation of Zn 2+ into the Li sublattice and enables a range of possible jump processes. Zn 2+ occupies the 48 h T5 site in the high-temperature F 43 m structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in I 4 Li 7 Zn 0.5 SiS 6 . The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10 -7 S cm -1 at room temperature and 4.3(4) × 10 -4 S cm -1 at 503 K. The transition between the ordered I 4 and disordered F 43 m structures is associated with a dramatic decrease in activation energy to 0.34(1) eV above 411 K. The incorporation of a small amount of Zn 2+ exercises dramatic control of Li order in Li 7 Zn 0.5 SiS 6 yielding a previously unseen distribution of Li sites, expanding our understanding of structure-property relationships in argyrodite materials., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Mixed anion materials and anion doping are very promising strategies to improve solid-state electrolyte properties by enabling an optimized balance between good electrochemical stability and high ionic conductivity. In this work, we present the discovery of a novel lithium aluminum sulfide-chloride phase, obtained by substitution of chloride for sulfur in Li 3 AlS 3 and Li 5 AlS 4 materials. The structure is strongly affected by the presence of chloride anions on the sulfur site, as the substitution was shown to be directly responsible for the stabilization of a higher symmetry phase presenting a large degree of cationic site disorder, as well as disordered octahedral lithium vacancies. The effect of disorder on the lithium conductivity properties was assessed by a combined experimental-theoretical approach. In particular, the conductivity is increased by a factor 10 3 compared to the pure sulfide phase. Although it remains moderate (10 -6 S·cm -1 ), ab initio molecular dynamics and maximum entropy (applied to neutron diffraction data) methods show that disorder leads to a 3D diffusion pathway, where Li atoms move thanks to a concerted mechanism. An understanding of the structure-property relationships is developed to determine the limiting factor governing lithium ion conductivity. This analysis, added to the strong step forward obtained in the determination of the dimensionality of diffusion, paves the way for accessing even higher conductivity in materials comprising an hcp anion arrangement., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

A hexagonal analogue, Li 6 SiO 4 Cl 2 , of the cubic lithium argyrodite family of solid electrolytes is isolated by a computation-experiment approach. We show that the argyrodite structure is equivalent to the cubic antiperovskite solid electrolyte structure through anion site and vacancy ordering within a cubic stacking of two close-packed layers. Construction of models that assemble these layers with the combination of hexagonal and cubic stacking motifs, both well known in the large family of perovskite structural variants, followed by energy minimization identifies Li 6 SiO 4 Cl 2 as a stable candidate composition. Synthesis and structure determination demonstrate that the material adopts the predicted lithium site-ordered structure with a low lithium conductivity of ∼10 -10 S cm -1 at room temperature and the predicted hexagonal argyrodite structure above an order-disorder transition at 469.3(1) K. This transition establishes dynamic Li site disorder analogous to that of cubic argyrodite solid electrolytes in hexagonal argyrodite Li 6 SiO 4 Cl 2 and increases Li-ion mobility observed via NMR and AC impedance spectroscopy. The compositional flexibility of both argyrodite and perovskite alongside this newly established structural connection, which enables the use of hexagonal and cubic stacking motifs, identifies a wealth of unexplored chemistry significant to the field of solid electrolytes., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

With the goal of finding new lithium solid electrolytes by a combined computational-experimental method, the exploration of the Li-Al-O-S phase field resulted in the discovery of a new sulfide Li 3 AlS 3 . The structure of the new phase was determined through an approach combining synchrotron X-ray and neutron diffraction with 6 Li and 27 Al magic-angle spinning nuclear magnetic resonance spectroscopy and revealed to be a highly ordered cationic polyhedral network within a sulfide anion hcp -type sublattice. The originality of the structure relies on the presence of Al 2 S 6 repeating dimer units consisting of two edge-shared Al tetrahedra. We find that, in this structure type consisting of alternating tetrahedral layers with Li-only polyhedra layers, the formation of these dimers is constrained by the Al/S ratio of 1/3. Moreover, by comparing this structure to similar phases such as Li 5 AlS 4 and Li 4.4 Al 0.2 Ge 0.3 S 4 ((Al + Ge)/S = 1/4), we discovered that the AlS 4 dimers not only influence atomic displacements and Li polyhedral distortions but also determine the overall Li polyhedral arrangement within the hcp lattice, leading to the presence of highly ordered vacancies in both the tetrahedral and Li-only layer. AC impedance measurements revealed a low lithium mobility, which is strongly impacted by the presence of ordered vacancies. Finally, a composition-structure-property relationship understanding was developed to explain the extent of lithium mobility in this structure type., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Framework oxides with the capacity to host mobile interstitial oxide anions are of interest as electrolytes in intermediate temperature solid oxide fuel cells (SOFCs). High performance materials of this type are currently limited to the anisotropic oxyapatite and melilite structure types. The langasite structure is based on a corner-shared tetrahedral network similar to that in melilite but is three-dimensionally connected by additional octahedral sites that bridge the layers by corner sharing. Using low-temperature synthesis, we introduce interstitial oxide charge carriers into the La 3 Ga 5- x Ge 1+ x O 14+ x /2 langasites, attaining a higher defect content than reported in the lower dimensional oxyapatite and melilite systems in La 3 Ga 3.5 Ge 2.5 O 14.75 ( x = 1.5). Neutron diffraction and multinuclear solid state 17 O and 71 Ga NMR, supported by DFT calculations, show that the excess oxygen is accommodated by the formation of a (Ge,Ga) 2 O 8 structural unit, formed from a pair of edge-sharing five-coordinated Ga/Ge square-based pyramidal sites bridged by the interstitial oxide and a strongly displaced framework oxide. This leads to more substantial local deformations of the structure than observed in the interstitial-doped melilite, enabled by the octahedral site whose primary coordination environment is little changed by formation of the pair of square-based pyramids from the originally tetrahedral sites. AC impedance spectroscopy on spark plasma sintered pellets showed that, despite its higher interstitial oxide content, the ionic conductivity of the La 3 Ga 5- x Ge 1+ x O 14+ x /2 langasite family is lower than that of the corresponding melilites La 1+ y Sr 1- y Ga 3 O 7+ y /2 . The cooperative structural relaxation that forms the interstitial-based (Ga,Ge) 2 O 8 units stabilizes higher defect concentrations than the single-site GaO 5 trigonal bipyramids found in melilite but effectively traps the charge carriers. This highlights the importance of controlling local structural relaxation in the design of new framework electrolytes and suggests that the propensity of a framework to form extended units around defects will influence its ability to generate high mobility interstitial carriers., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)