High-pressure synthesis of A-site ordered perovskite PbMn3(CrMn3)O12 with long-range antiferromagnetic ordering and a spin glass transition.

An AA'3B4O12-type perovskite oxide PbMn3(CrMn3)O12 was synthesized by high-pressure solid-state reactions at 8 GPa and 1373 K. Synchrotron X-ray diffraction shows a cubic crystal structure with the space group Im3̄. The charge states are verified by X-ray photoelectron spectroscopy to be PbMn3+3(Cr3+Mn3+2Mn4+)O12, where the Pb2+ and Mn3+ are 1 : 3 ordered respectively at A and A' sites, while the Cr3+, Mn3+ and Mn4+ are disorderly distributed at the B site. PbMn3(CrMn3)O12 features a long-range antiferromagnetic order of A'-site Mn3+ spins at about 66 K and a subsequent spin glass transition around 36 K due to the randomly distributed Cr3+, Mn3+, and Mn4+ cations at the B site. This unique stepwise order of A' and B-site spins indicates weak A'-B site spin interactions, which are dominated by the difference in the B-site Mn3+/Ni2+ and Mn4+ number in the quadruple perovskites AMn3B4O12.

Hexagonal Halide Perovskite Cs2LiInCl6: Cation Ordering, Face-Shared Octahedral Trimers and Mn2+ Luminescence.

The In-based double perovskite halides have been widely studied for promising optical-electric applications. The halide hexagonal perovskite Cs2LiInCl6 was isolated using solid-state reactions and investigated using X-ray diffraction and solid-state NMR spectra. The material adopts a 12-layered hexagonal structure (12R) consisting of layered cationic orders driven by the cationic charge difference and has Li+ cations in the terminal site and In3+ in the central site of face-shared octahedron trimers. Such a cationic ordering pattern is stabilized by electrostatic repulsions between the next-nearest neighboring cations in the trimers. The LiCl6 octahedron displays large distortion and is confirmed by 7Li SSNMR in the Cs2LiInCl6. The Cs2LiInCl6 material has a direct bandgap of ~ 4.98 eV. The Cs2LiInCl6: Mn displays redshift luminescence (centered at ~610 - 622 nm) from the substituted Mn2+ emission in octahedron with larger PLQY (17.8%-48%) compared with that of Cs2NaInCl6: Mn2+.  The Mn-doped materials show luminescent concentration quenching and thermal quenching. The composition Cs2Li0.99In0.99Mn0.02Cl6 exhibits the highest PL intensity, a maximum PLQY of 48%, and high luminescent retention rate of ~ 86% below 400 K and is suitable for application for pc-LED. These findings contribute to our understanding of the chloride perovskites and hold potential for widespread optical applications.

Bulk Synthesis and Transport Properties of Rocksalt-Type Ti1-xMgxN Solid Solution.

Owing to the decomposition issue of Mg3N2, many Mg-containing ternary nitrides were prepared by the hybrid arc evaporation/sputtering technique, which has the advantages including access to the unstable phases, high film purity, good density, and uniform film formation but the drawbacks of cost and long production cycle for the required targets. In the present study, we demonstrate that rocksalt-type Ti1-xMgxN, previously prepared exclusively by the thin-film methods, can be obtained as a disordered cubic phase by the conventional bulk synthesis method through a facile one-step reaction. Employing a combination of experimental measurements and theoretical calculations, we discover that the crystal structure and the physical properties of the as-synthesized Ti1-xMgxN solid solution can be tuned by the Mg content; a metal-to-semiconductor transition and also suppression of the superconducting phase transition are observed when the Mg and Ti content ratio increases to close to 1. Theoretical calculations indicate that the lattice distortions in the disordered Ti1-xMgxN induced by the different ionic sizes of Mg and Ti increase with the Mg content and the disordered cubic rocksalt structures become unstable. The ordered rocksalt-derived structures are more stable than the disordered rocksalt structures on composition x = 0.5. Furthermore, electronic structure calculations provide an insight into the low resistance behavior and transport property evolution of Ti1-xMgxN from the aspects of Ti3+ content, the cation distribution, or nitrogen defects. The results highlight the feasibility of the simple bulk route for the successful synthesis of Mg-containing ternary nitrides and the heterovalent ion substitution on modulating the properties of nitrides.

Magnetic clusters and ferromagnetic spin glass in the novel hexagonal perovskite 12R-Ba4SbMn3O12.

A 12-layer hexagonal perovskite Ba4SbMn3O12 (space group: R3̄m; a = 5.72733(3) Å, and c = 28.1770(3) Å) has been synthesized by high-temperature solid-state reactions and studied using powder X-ray and neutron diffraction and magnetization measurements. This 12R polytype structure contains one corner-sharing (Sb, Mn)O6 octahedron and a trimer of face-sharing MnO6 octahedra per formula unit. Ba4SbMn3O12 displays a paramagnetic state of the Mn3 magnetic cluster at 100-200 K, which partially disassociates into individual Mn ions at 250-300 K. The ferromagnetic interaction between these Mn3 clusters is mainly mediated by Mn3+ at the M1 site, leading to dynamic ferromagnetic clusters below T D = ∼70 K and ferromagnetic spin freezing transition at T g = ∼11.5 K. The stability of Mn3 magnetic clusters in the 12R polytypes is related to the intracluster Mn-Mn distance.

Theoretical and Experimental Studies of Gallate Melilite Electrides from Topotactic Reduction of Interstitial Oxide Ion Conductors.

A nonstoichiometric La1.5Sr0.5Ga3O7.25 melilite oxide ion conductor features active interstitial oxygen defects in its pentagonal rings with high mobility. In this study, electron localization function calculated by density functional theory indicated that the interstitial oxide ions located in the pentagonal rings of gallate melilites may be removed and replaced by electron anions that are confined within the pentagonal rings, which would therefore convert the melilite interstitial oxide ion conductor into a zero-dimensional (0D) electride. The more active interstitial oxide ions, compared to the framework oxide ions, make the La1.5Sr0.5Ga3O7.25 melilite structure more reducible by CaH2 using topotactic reduction, in contrast to the hardly reducible nature of parent LaSrGa3O7. The topotactic reduction enhances the bulk electronic conduction (σ ∼ 0.003 S/cm at 400 °C) by ∼ 1 order of magnitude for La1.5Sr0.5Ga3O7.25. The oxygen loss in the melilite structure was verified and most likely took place on the active interstitial oxide ions. The identified confinement space for electronic anions in melilite interstitial oxide ion conductors presented here provides a strategy to access inorganic electrides from interstitial oxide ion conductor electrolytes.

Correlation of Tunable CoSi4 Tetrahedron with the Superconducting Properties of LaCoSi.

It is known that as the FeAs4 tetrahedron in the Fe-based superconductor is close to the regular tetrahedron, critical temperature (Tc) can be greatly increased. Recently, a Co-based superconductor of LaCoSi (4 K) with "111" structure was found. In this work, we improve the Tc of LaCoSi through structural regulation. Tc can be increased by the chemical substitution of Co by Fe, while the superconductivity is suppressed by the Ni substitution. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that the change of the Si-Co-Si bond angles of the CoSi4 tetrahedron is possibly responsible for the determination of superconducting properties. The Fe chemical substitution is favorable for the formation of the regular tetrahedron of CoSi4. The present new Co-based superconductor of LaCoSi provides a possible method to enhance the superconductivity performance of the Co-based superconductors via controlling Co-based tetrahedra similar to those well established in the Fe-based superconductors.

Narrow-band red emitting oxonitridosilicate phosphor La4-xSr2+xSi5N12-xOx:Pr3+ (x≈ 1.69).

The new oxonitridosilicates Ln4-xSr2+xSi5N12-xOx (Ln = La, Ce) were synthesized by high temperature solid-state reactions. The crystal structures were solved and refined from both single-crystal and powder X-ray diffraction data. These oxonitridosilicate compounds crystallize in the monoclinic space group P21/n (no. 14) and exhibit a double-layer structure made up of corner-sharing Si(O/N)4 tetrahedra. When excited with near-UV and blue light, the Pr3+ doped La2.31Sr3.69Si5N10.31O1.69 phosphor shows a narrow-band red emission peaking at 625 nm with a full width at half-maximum of 40 nm.

Molecule-like cluster magnetism and cationic order in the new hexagonal perovskite Ba4Sn1.1Mn2.9O12.

The new hexagonal perovskite phase of composition Ba4Sn1.1Mn2.9O12 has been synthesized by solid-state reactions at 1673 K. The crystal structure has been investigated using X-ray and neutron diffraction. The hexagonal perovskite structure has an ordered arrangement of Sn and Mn ions on the corner-sharing octahedral centers and the face-sharing octahedral centers respectively. Short Mn-Mn distances have been evidenced in the face-sharing trimer of MnO6 octahedra. The magnetic susceptibility shows magnetic cluster behavior, with cluster formation temperature ∼220 K. Antiferromagnetic order has been observed at T N ∼ 6 K. Ba4Sn1.1Mn2.9O12 is a semiconductor with a transport activation energy of 0.61 eV.

Reply to the 'Comment on "Uncommon structural and bonding properties in Ag16B4O10" by A. Lobato, Miguel Á. Salvadó, and J. Manuel Recio, Chem. Sci., 2021, 12, DOI: 10.1039/D1SC02152D.

Where are the excess electrons in Ag16B4O10?

Shift-Twin Option in Eight-Layer Hexagonal Perovskite Niobates Ba8MNb6O24.

Two new eight-layer hexagonal perovskites with the composition Ba8MNb6O24 (M = Fe and Cu) are synthesized by solid-state reaction at 1350-1400 °C. Their crystal structures have been investigated using X-ray and electron diffractions as well as high-resolution transmission electron microscopy. Although both compounds have similar M2+ size, Ba8FeNb6O24 and Ba8CuNb6O24 adopt shifted and twinned structures, respectively. Through comparison with the reported shifted Ba8MNb6O24 (M = Mn, Co, and Zn) and twinned Ba8NiNb6O24 as well as inexistent Ba8Mg(Nb/Ta)6O24, we elucidate that the twin-shift competition of Ba8MNb6O24 family could be related with multiple chemical factors including tolerance factors, B-cationic size difference, entropy variation with B-cation and vacancy disorder, Jahn-Teller distortion, and FSO B-B d orbit interactions.

Mn2+-Mn2+ Magnetic Coupling Effect on Photoluminescence Revealed by Photomagnetism in CsMnCl3.

The magnetic coupling interaction of Mn2+-Mn2+ in Mn2+-included phosphors could induce a shorter emission decay time, compared with that of isolated Mn2+, which could overcome the photoluminescence (PL) saturation when stimulated by a high photon flux due to the long lifetime of the Mn2+ excited state. However, few studies have directly proved the Mn2+-Mn2+ coupling effect on the PL decay. In this paper, the effect on PL of CsMnCl3 (CMC) and its hydrates is revealed by photomagnetism results, excluding the interference effects of site symmetry and phonon energy. The antiferromagnetic interaction of the CMC is larger when Mn2+ at a photoexcited state than at a dark state, which is contrary to the hydrates with weak Mn2+-Mn2+ interaction. This research not only helps researchers to understand the fundamental optical process but also is instructive for designing high performance Mn2+-doped phosphors in the field of displays and lighting.

Trigonal-Planar Low-Spin Co2+ in a Layered Mixed-Polyhedral Network from Topotactic Reduction.

Topotactic reduction of the perovskite oxide TbBaCo2O5.5 with CaH2 leads to a new crystalline phase TbBaCo2O4.5, adopting a 2 × 2 × 1 superstructure compared to TbBaCo2O5.5. The structure consists of a corner-shared network of square pyramidal CoO5 and trigonal planar CoO3 units. Magnetic susceptibility and variable temperature neutron diffraction data reveal that TbBaCo2O4.5 adopts a G-type antiferromagnetically ordered structure (TN ∼ 322 K). The ordered moments are consistent with the presence of low-spin Co2+ (S = 1/2) in trigonal-planar coordination and high-spin Co2+ centers in square pyramidal coordination. TbBaCo2O4.5 shows lower conductivity than TbBaCo2O5.5, which is consistent with the p-type conduction behavior. The unique anion vacancy arrangements in TbBaCo2O4.5 further complement the role of A-cations in controlling the oxygen vacancy distribution in LnBaCo2O5+δ series and demonstrate more opportunity to tune the structural and physical properties based on cationic and anionic lattice coupling.

Uncommon structural and bonding properties in Ag16B4O10.

Ag16B4O10 has been obtained as a coarse crystalline material via hydrothermal synthesis, and was characterized by X-ray single crystal and powder diffraction, conductivity and magnetic susceptibility measurements, as well as by DFT based theoretical analyses. Neither composition nor crystal structure nor valence electron counts can be fully rationalized by applying known bonding schemes. While the rare cage anion (B4O10)8- is electron precise, and reflects standard bonding properties, the silver ion substructure necessarily has to accommodate eight excess electrons per formula unit, (Ag+)16(B3+)4(O2-)10 × 8e-, rendering the compound sub-valent with respect to silver. However, the phenomena commonly associated with sub-valence metal (partial) structures are not perceptible in this case. Experimentally, the compound has been found to be semiconducting and diamagnetic, ruling out the presence of itinerant electrons; hence the excess electrons have to localize pairwise. However, no pairwise contractions of silver atoms are realized in the structure, thus excluding formation of 2e-2c bonds. Rather, cluster-like aggregates of an approximately tetrahedral shape exist where the Ag-Ag separations are significantly smaller than in elemental silver. The number of these subunits per formula is four, thus matching the required number of sites for pairwise nesting of eight excess electrons. This scenario has been corroborated by computational analyses of the densities of states and electron localization function (ELF), which clearly indicate the presence of an attractor within the shrunken tetrahedral voids in the silver substructure. However, one bonding electron pair of s and p type skeleton electrons per cluster unit is extremely low, and the significant propensity to form and the thermal stability of the title compound suggest d10-d10 bonding interactions to strengthen the inter-cluster bonding in a synergistic fashion. With the present state of knowledge, such a particular bonding pattern appears to be a singular feature of the oxide chemistry of silver; however, as indicated by analogous findings in related silver oxides, it is evolving as a general one.

An FeF(3)·0.5H2O polytype: a microporous framework compound with intersecting tunnels for Li and Na batteries.

To improve the energy/power density of energy storage materials, numerous efforts have focused on the exploration of new structure prototypes, in particular metal-organic fameworks, Prussian blue analogues, open-framework oxides, and polyanion salts. Here we report a novel pyrochlore phase that appears to be useful as a high-capacity cathode for Li and Na batteries. It is an iron fluoride polymorph characterized by an intersecting tunnel structure, providing the space for accommodation and transport of Li and Na ions. It is prepared using hydrolyzable ionic liquids, which serve as reaction educts and structure-directing agents not only as far as the chemical structure is concerned but also in terms of morphology (shape, defect structure, electrode network structure). A capacity higher than 220 mA h g(-1) (for Li and Na storage) and a lifetime of at least 300 cycles (for Li storage) are demonstrated.

Structural and magnetic properties of Ba0.7Sr0.3Ru(1-x)Mn(x)O3 hexagonal perovskites.

The structures and properties of Ba(0.7)Sr(0.3)Ru(1-x)Mn(x)O(3) perovskites have been investigated in samples prepared at 1300 degrees C in air. Two polytypes are found, a 6H phase for 0.2 < or = x < or = 0.4 and a 4H type for 0.6 < or = x < or = 1. The cell parameters and volume vary linearly in both solid solution ranges. Spin-freezing transitions up to 60 K are observed for the 6H samples, but the 4H materials show high temperature Néel transitions at 210 to 280 K.