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Natrium super ionic conductor (NASICON) compounds form a rich and highly chemically tunable family of crystalline materials that are of widespread interest because they include exemplars with high ionic conductivity, low thermal expansion, and redox tunability. This makes them suitable candidates for applications ranging from solid-state batteries to nuclear waste storage materials. The key to an understanding of these properties, including the origins of effective cation transport and low, anisotropic (and sometimes negative) thermal expansion, lies in the lattice dynamics associated with specific details of the crystal structure. Here we closely examine the prototypical NASICON compound, NaZr2(PO4)3, and obtain detailed insights into such behavior via variable-temperature neutron diffraction and 23Na and 31P solid-state NMR studies, coupled with comprehensive density functional theory-based calculations of NMR parameters. Temperature-dependent NMR studies yield some surprising trends in the chemical shifts and the quadrupolar coupling constants that are not captured by computation unless the underlying vibrational modes of the crystal are explicitly taken into account. Furthermore, the trajectories of the sodium, zirconium, and oxygen atoms in our dynamical simulations show good qualitative agreement with the anisotropic thermal parameters obtained at higher temperatures by neutron diffraction. The work presented here widens the utility of NMR crystallography to include thermal effects as a unique probe of interesting lattice dynamics in functional materials.

The guest-dependent flexibility of the pillared-layered metal-organic framework (MOF), Zn2bdc2dabco·X(guest), where guest = EtOH, DMF or benzene, has been examined by high-pressure single crystal X-ray diffraction. A pressure-induced structural phase transition is found for the EtOH- and DMF-included frameworks during compression in a hydrostatic medium of the guest species, which is dependent upon the nature and quantity of the guest in the channels. The EtOH-included material undergoes a phase transition from P4/mmm to C2/m at 0.69 GPa, which is accompanied by a change in the pore shape from square to rhombus via super-filling of the pores. The DMF-included material undergoes a guest-mediated phase transition from I4/mcm to P4/mmm at 0.33 GPa via disordering of the DMF guest. In contrast, the benzene-included framework features a structure with rhombus-shaped channels at ambient pressure and shows direct compression under hydrostatic pressure. These results demonstrate the large influence of guest molecules on the high-pressure phase behavior of flexible MOFs. Guest-mediated framework flexibility is useful for engineering MOFs with bespoke pore shapes and compressibility.

Although metal-organic frameworks (MOFs) are being widely used to derive functional nanomaterials through pyrolysis, the actual mechanisms involved remain unclear. In the limited studies to date, elemental metallic species are found to be the initial products, which limits the variety of MOF-derived nanomaterials. Here, the pyrolysis of a manganese triazolate MOF is examined carefully in terms of phase transformation, reaction pathways, and morphology evolution in different conditions. Surprisingly, the formation of metal is not detected when manganese triazolate is pyrolyzed in an oxygen-free environment. Instead, a direct transformation into nanoparticles of manganese nitride, Mn2N x embedded in N-doped graphitic carbon took place. The electrically conductive Mn2N x nanoparticles show much better air stability than bulk samples and exhibit promising electrocatalytic performance for the oxygen reduction reaction. The findings on pyrolysis mechanisms expand the potential of MOF as a precursor to derive more functional nanomaterials.

Phosphorene, monolayer or few-layer black phosphorus, exhibits fascinating anisotropic properties and shows interesting semiconducting behavior. The synthesis of phosphorene nanosheets is still a hot topic, including the shaping of its two-dimensional structure into nanoribbons or nanobelts. Here we report electrochemical unzipping of single crystalline black phosphorus into zigzag-phosphorene nanobelts, as well as nanosheets and quantum dots, via an oxygen-driven mechanism. The experimental results agree well with our theoretical calculations. The calculation for the unzipping mechanism study suggests that interstitial oxygen-pairs are the critical intermediate species for generating zigzag-phosphorene nanobelts. Although phosphorene oxidation has been reported, lengthwise cutting is hitherto unreported. Our discovery of phosphorene cut upon oxidation represents a previously unknown mechanism for the formation of various dimensions of phosphorene nanostructures, especially zigzag-phosphorene nanobelts. It opens up a way for studying the quantum effects and electronic properties of zigzag-phosphorene nanobelts.

Sodium-ion batteries (SIBs) are promising power sources due to the low cost and abundance of battery-grade sodium resources, while practical SIBs suffer from intrinsically sluggish diffusion kinetics and severe volume changes of electrode materials. Metal-organic framework (MOFs) derived carbonaceous metal compound offer promising applications in electrode materials due to their tailorable composition, nanostructure, chemical and physical properties. Here, we fabricated hierarchical MOF-derived carbonaceous nickel selenides with bi-phase composition for enhanced sodium storage capability. As MOF formation time increases, the pyrolyzed and selenized products gradually transform from a single-phase Ni3Se4 into bi-phase NiSex then single-phase NiSe2, with concomitant morphological evolution from solid spheres into hierarchical urchin-like yolk-shell structures. As SIBs anodes, bi-phase NiSex@C/CNT-10h (10 h of hydrothermal synthesis time) exhibits a high specific capacity of 387.1 mAh/g at 0.1 A/g, long cycling stability of 306.3 mAh/g at a moderately high current density of 1 A/g after 2,000 cycles. Computational simulation further proves the lattice mismatch at the phase boundary facilitates more interstitial space for sodium storage. Our understanding of the phase boundary engineering of transformed MOFs and their morphological evolution is conducive to fabricate novel composites/hybrids for applications in batteries, catalysis, sensors, and environmental remediation.

Following the recent discovery of a new family of hybrid ABX3 perovskites where X=(H2 POO)- (hypophosphite), this work reports a facile synthesis for mixed X-site formate perovskites of composition [GUA]Mn(HCOO)3-x (H2 POO)x , with two crystallographically distinct, partially ordered intermediate phases with x=0.84 and 1.53, corresponding to ca. 30 and 50 mol % hypophosphite, respectively. These phases are characterised by single-crystal XRD and solid-state NMR spectroscopy, and their magnetic properties are reported.

Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for separation, gas adsorption, catalysis and biotechnology. Their practical application, however, can be hampered by their structural instability in humid acidic conditions. Here, guided by density functional theory calculations, we demonstrate that the acidic stability of two polymorphic ZIFs (i.e. ZIF-8 and ZIF-L) can be enhanced by incorporating functional groups on polypeptides or DNA. A range of complementary synchrotron investigations into the local chemical structure and bonding environment suggest that the enhanced acidic stability arises from the newly-established coordinative interactions between the Zn centers and the inserted carboxylate (for polypeptides) or phosphate (for DNA) groups, which both have lower pKas than the imidazolate ligand. With functional biomolecular homologues (i.e. enzymes), we demonstrate a symbiotic stability reinforcement effect, i.e. the encapsulated biomolecules stabilize the ZIF matrix while the ZIF exoskeleton protects the enzyme from denaturation.

In a search for Pb-free photovoltaic materials, a double perovskite Cs2AgSbBr6 with an indirect optical bandgap of 1.64 eV has been synthesized. Single crystal X-ray diffraction determined the space group as Fm3[combining macron]m with a = 11.1583(7) Å. The black, as-synthesised compound turned brown after heat treatment at 480 K while the symmetry and crystallinity were preserved. X-ray photoelectron spectroscopy indicated the existence of Sb5+ in the black crystals, suggesting that the dark colour arises from the Sb3+-Sb5+ charge transfer. Furthermore, UV visible spectroscopy and density functional theory calculations have been applied to probe the optical properties and electronic structure.

Trivalent metal hypophosphites with the general formula M(H2PO2)3 (M = V, Al, Ga) adopt the ReO3 structure, with each compound displaying two structural polymorphs. High-pressure synchrotron X-ray studies reveal a pressure-driven phase transition in Ga(H2PO2)3 that can be understood on the basis of ab initio thermodynamics.

The physicochemical properties of the potassium neptunate K2NpO4 have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L3 edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported for the first time. The Np(VI) valence state has been confirmed by the XANES data, and the absorption edge threshold of the XANES spectrum has been correlated to the Mössbauer isomer shift value reported in the literature. The standard entropy and heat capacity of K2NpO4 have been derived at 298.15 K from the low-temperature heat capacity data. The latter suggest the existence of a magnetic ordering transition around 25.9 K, most probably of the ferromagnetic type.

The discovery of lead-free hybrid double perovskites provides a viable approach in the search for stable and environmentally benign photovoltaic materials as alternatives to the lead-containing systems such as MAPbX3 (X = Cl, Br, I). Follow-ing our recent reports of (MA)2KBiCl6 and (MA)2TlBiBr6, we have now synthesized a hybrid double perovskite, (MA)2AgBiBr6, that has a low band gap of 2.02eV and is rela-tively stable and non-toxic. Its electronic structure and me-chanical and optical properties are investigated with a com-bination of experimental studies and density functional theory calculations.

Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to a remarkable breakthrough in photovoltaic devices. However, due to the environmental and stability concerns of the heavy metal, lead, in these perovskite based solar cells, research in the non-lead perovskite structures have been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH4)3Bi2I9, was prepared in solution and the structure was solved by single crystal X-ray diffraction. The results from DFT calculations showed the significant lone pair effect of the bismuth ion and the band gap was measured as around 2.04 eV, which is lower than the band gap of CH3NH3PbBr3. Conductivity measurement was also performed to examine the potential in the applications as an alternative to the lead containing perovskites.

The Giant Magellan Telescope (GMT) consists of seven 8.365 m segments with a separation of 0.345 m. A uniquechallenge for GMT lies in phasing these segments and, in particular, how to measure segment piston optically.In this paper, we present a results of a phasing strategy using a non-redundant pupil mask. We show how thismethod can be extended to measure segment piston differences of more than half a wave by using broadbandlight.

Understanding the formation of stellar and planetary systems is one of the great challenges of contemporary astrophysics. This thesis describes progress towards understanding these processes, through advancement of techniques to enable high resolution imaging of faint companions and other structures in the immediate environs of young stars. To ensure optimal performance in an era of large segmented telescopes, techniques to precisely cophase the mirror segments are required. In this thesis we propose the Fizeau Interferometric Cophasing of Segmented Mirrors algorithm, and present the results of testing both numerically and through experiment. We help to rectify a lack of observational evidence with which to test brown dwarf evolutionary models, by laying the foundation for an orbital monitoring survey of 19 brown dwarf binary systems and reporting the discovery of an additional 7 low mass companions to intermediate mass stars. We perform a Non-Redundant Masking (NRM) survey targeting the 1\,Myr old Ophiuchus star forming region. Both binary statistics and the relationship between multiplicity and the presence of a circumstellar disk are explored, providing many results similar to those from older regions. This helps frame the time evolution of effects related to dynamical interactions in binary systems, and the timescale of disk dissipation, with profound implications for giant planet formation. In thesis we also present the results of commissioning for the Gemini Planet Imager Non-Redundant Masking mode. These results indicate that the addition of an Extreme Adaptive Optics systems has substantially improved the performance of NRM compared to previous instruments. Finally, the transition disk T Cha is studied with multi-epoch NRM data, showing that the signal previously interpreted as a planetary companion is more likely to be the result of forward scattering from the inclined outer disk.

Near or less than 10% Nb substitution on the Ti site in perovskite SrTiO$_3$ results in metallic behavior, in contrast to what is seen in BaTiO$_3$. Given the nearly identical structure and electron counts of the two materials, the distinct ground states for low substitution have been a long-standing puzzle. Here we find from neutron studies of average and local structure, the subtle yet critical difference that we believe underpins the distinct electronic properties in these fascinating materials. While SrTi$_{0.875}$Nb_${0.125}$O$_3$ possesses a distorted non-cubic structure at 15 K, the BO$_6$ octahedra in the structure are regular. BaTi$_{0.875}$Nb$_{0.125}$O$_3$ on the other hand shows evidence for local cation off-centering whilst retaining a cubic structure., Comment: 4 pages, 5 figures

Three-dimensional carbon-based structures have proven useful for tailoring material properties in structural mechanical and energy storage applications. One approach to obtain them has been by carbonization of selected metal-organic frameworks (MOFs) with catalytic metals, but this is not applicable to most common MOF structures. Here, we present a strategy to transform common MOFs, by guest inclusions and high-temperature MOF-guest interactions, into complex carbon-based, diatom-like, hierarchical structures (named for the morphological similarities with the naturally existing diatomaceous species). As an example, we introduce metal salt guests into HKUST-1-type MOFs to generate a family of carbon-based nano-diatoms with two to four levels of structural hierarchy. We report control of the morphology by simple changes in the chemistry of the MOF and guest, with implications for the formation mechanisms. We demonstrate that one of these structures has unique advantages as a fast-charging lithium-ion battery anode. The tunability of composition should enable further studies of reaction mechanisms and result in the growth of a myriad of unprecedented carbon-based structures from the enormous variety of currently available MOF-guest candidates.

Spatially resolving the immediate surroundings of young stars is a key challenge for the planet formation community. SPHERE on the VLT represents an important step forward by increasing the opportunities offered by optical or near-infrared imaging instruments to image protoplanetary discs. The Guaranteed Time Observation Disc team has concentrated much of its efforts on polarimetric differential imaging, a technique that enables the efficient removal of stellar light and thus facilitates the detection of light scattered by the disc within a few au from the central star. These images reveal intriguing complex disc structures and diverse morphological features that are possibly caused by ongoing planet formation in the disc. An overview of the recent advances enabled by SPHERE is presented., Published in The Messenger vol. 169, pp. 32-37, September 2017.

Geometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal-organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO2 catalyst (RuO2@MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO2-supported RuO2 (RuO2/SiO2). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides).

Funder: National Key R (D Program of China);2016YFA0200200, Funder: National Key D Program of China (2016YFA0200200) and National Natural Science Foundation of China (Nos. 51672154), Phosphorene, monolayer or few-layer black phosphorus, exhibits fascinating anisotropic properties and shows interesting semiconducting behavior. The synthesis of phosphorene nanosheets is still a hot topic, including the shaping of its two-dimensional structure into nanoribbons or nanobelts. Here we report electrochemical unzipping of single crystalline black phosphorus into zigzag-phosphorene nanobelts, as well as nanosheets and quantum dots, via an oxygen-driven mechanism. The experimental results agree well with our theoretical calculations. The calculation for the unzipping mechanism study suggests that interstitial oxygen-pairs are the critical intermediate species for generating zigzag-phosphorene nanobelts. Although phosphorene oxidation has been reported, lengthwise cutting is hitherto unreported. Our discovery of phosphorene cut upon oxidation represents a previously unknown mechanism for the formation of various dimensions of phosphorene nanostructures, especially zigzag-phosphorene nanobelts. It opens up a way for studying the quantum effects and electronic properties of zigzag-phosphorene nanobelts.

Geometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal–organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO2 catalyst (RuO2@MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO2-supported RuO2 (RuO2/SiO2). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides)., Loading guests inside the pre-existing pores of nanoporous hosts remains challenging. Here, the authors introduce a rational route for incorporation of guest compounds into an arbitrary nanoporous host, enabling the investigation of multiple host-guest systems with surprising functionalities.