Unusual Pressure-Induced Self-Trapped Exciton to Free Exciton Transfer in Chiral 2D Lead Bromide Perovskites.

The phenomenon of pressure-induced emission alterations related to complex excitonic dynamics in 2D lead halide perovskites (LHPs) has gained considerable attention for understanding their structure-property relationship and obtaining inaccessible luminescence under ambient conditions. However, the well-known pressure-induced emissions are limited to the formation of self-trapped excitons (STEs) due to the structural distortion under compression, which goes against the advantage of the highly pure emission of LHPs. Here, the pressure-induced detrapping from STEs to free excitons (FEs) accompanied by the dramatic transition from broadband orangish emission to narrow blue emission has been achieved in chiral 2D LHPs and - and -[4MeOPEA]PbBr, (4MeOPEA = 4-methoxy-α-methylbenzylammonium).

Origin of Ferroelectricity in Two Prototypical Hybrid Organic-Inorganic Perovskites.

Hybrid organic-inorganic perovskite (HOIP) ferroelectrics are attracting considerable interest because of their high performance, ease of synthesis, and lightweight. However, the intrinsic thermodynamic origins of their ferroelectric transitions remain insufficiently understood. Here, we identify the nature of the ferroelectric phase transitions in displacive [(CH)NH][Mn(N)] and order-disorder type [(CH)NH][Mn(HCOO)] via spatially resolved structural analysis and lattice dynamics calculations.

Group-theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS)-pyrrhotite (FeS).

A group-theoretical framework to describe vacancy ordering and magnetism in the FeS system is developed. This framework is used to determine the sequence of crystal structures consistent with the observed magnetic structures of troilite (FeS), and to determine the crystallographic nature of the low-temperature Besnus transition in FeS. It is concluded that the Besnus transition is a magnetically driven transition characterized by the rotation of the moments out of the crystallographic plane to which they are confined above the transition, accompanied by small atomic displacements that lower the symmetry from monoclinic to triclinic at low temperatures.

An algebraic approach to cooperative rotations in networks of interconnected rigid units.

Crystalline solids consisting of three-dimensional networks of interconnected rigid units are ubiquitous amongst functional materials. In many cases, application-critical properties are sensitive to rigid-unit rotations at low temperature, high pressure or specific stoichiometry. The shared atoms that connect rigid units impose severe constraints on any rotational degrees of freedom, which must then be cooperative throughout the entire network.

An Unusual Phase Transition Driven by Vibrational Entropy Changes in a Hybrid Organic-Inorganic Perovskite.

The driving forces for the phase transitions of ABX hybrid organic-inorganic perovskites have been limited to the octahedral tilting, order-disorder, and displacement. Now, a complex structural phase transition has been explored in a HOIP, [CH NH ][Mn(N ) ], based on structural characterizations and ab initio lattice dynamics calculations. This unusual first-order phase transition between two ordered phases at about 265 K is primarily driven by changes in the collective atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting.

Guest-Activated Forbidden Tilts in a Molecular Perovskite Analogue.

The manipulation of distortions in perovskite structures is critical to tailoring the properties of these materials for a variety of applications. Here we demonstrate a violation of established octahedral tilt rules in the double perovskite analogue (NH4)2SrFe(CN)6·2H2O. The forbidden tilt pattern we observe arises through coupling to hydration-driven Jahn-Teller-like distortions of the Sr coordination environment.

Psychospiritual Resiliency: Enhancing Mental Health and Ecclesiastical Collaboration in Caring for Those Experiencing Dissociative Phenomena.

Trauma can oftentimes be a catalyst for changes in an individual's religious and spiritual beliefs. Beliefs about the cause of the trauma, for instance, may include attributions of possessing spirits, and are to be found in an increasingly pluralistic and multicultural society. Such preternatural explanations may be referred to as dissociative identity disorder, possession form.

Octahedral tilting in the tungsten bronzes.

Possibilities for 'simple' octahedral tilting in the hexagonal and tetragonal tungsten bronzes (HTB and TTB) have been examined, making use of group theory as implemented in the computer program ISOTROPY. For HTB, there is one obvious tilting pattern, leading to a structure in space group P6₃/mmc. This differs from the space group P6₃/mcm frequently quoted from X-ray studies – these studies have in effect detected only displacements of the W cations from the centres of the WO6 octahedra.

Mechanical tunability via hydrogen bonding in metal-organic frameworks with the perovskite architecture.

Two analogous metal-organic frameworks (MOFs) with the perovskite architecture, [C(NH2)3][Mn(HCOO)3] (1) and [(CH2)3NH2][Mn(HCOO)3] (2), exhibit significantly different mechanical properties. The marked difference is attributed to their distinct modes of hydrogen bonding between the A-site amine cation and the anionic framework. The stronger cross-linking hydrogen bonding in 1 gives rise to Young's moduli and hardnesses that are up to twice those in 2, while the thermal expansion is substantially smaller.

Crystal and magnetic structures of hexagonal YMnO3.

The available data on the structural and magnetic transitions in multiferroic hexagonal YMnO3 have been reviewed, first making use of the computer programs from the group theoretical ISOTROPY software suite to list possible crystal and magnetic structures, then taking into account the capability of neutron diffraction and other physical methods to distinguish them. This leads to a clear view of the transformation sequence, as follows. Hexagonal YMnO3 is paraelectric in P63/mmc at elevated temperatures, and undergoes a single structural transition on cooling through 1250 K to a ferrielectric phase in P63cm that is retained through room temperature.

Elastic and anelastic relaxations accompanying magnetic ordering and spin-flop transitions in hematite, Fe2O3.

Hematite, Fe(2)O(3), provides in principle a model system for multiferroic (ferromagnetic/ferroelastic) behavior at low levels of strain coupling. The elastic and anelastic behavior associated with magnetic phase transitions in a natural polycrystalline sample have therefore been studied by resonant ultrasound spectroscopy (RUS) in the temperature range from 11 to 1072 K. Small changes in softening and attenuation are interpreted in terms of weak but significant coupling of symmetry-breaking and non-symmetry-breaking strains with magnetic order parameters in the structural sequence R3(¯)c1'-->C2/c-->R3(¯)c.

Symmetry analysis of the structural and magnetic phase transitions in 122 iron arsenides.

It is evident from the literature that the 122 iron arsenides, XFe(2)As(2) with X = Ca, Sr, Ba or Eu, undergo one or more phase transitions from a higher-temperature paramagnetic tetragonal structure in grey group I4/mmm1' to an antiferromagnetic structure with magnetic space group C(A)mca. Symmetry analysis is used to enumerate the possibilities for the transition (or transitions) between the higher- and lower-symmetry structures, and the results are used as a basis for comment on published experimental results.

A linear-quadratic order parameter coupling model for magnetoelastic phase transitions in Fe(1-x)O and MnO.

The combined structural and antiferromagnetic phase transition in wüstite, Fe(1-x)O, at the Néel temperature, T(N) ~ 195 K, is treated in terms of coupling between two macroscopic order parameters related to separate discrete instabilities. These each couple with a rhombohedral shear strain to give an indirect mechanism of linear (structural)-quadratic (magnetic) coupling between them. Based on patterns of lattice parameter and magnetic ordering data from the literature, it appears that the overall behaviour matches the general pattern of linear-quadratic coupling for a system with two rather similar instability temperatures.

X-ray absorption and neutron diffraction studies of (Sr(1 - x)Ce(x))MnO3: transition from coherent to incoherent static Jahn-Teller distortions.

We have carried out Ce L- and Mn K-edge x-ray absorption near edge structure (XANES) measurements to experimentally determine the oxidation states of both Ce and Mn in (Sr(1 - x)Ce(x))MnO(3) (x = 0.1-0.4).

Characterization of age-related changes in bovine CD8+ T-cells.

Evaluation of the changes induced by immunological interventions requires a baseline against which to compare those changes. The age-related changes in the CD8(+) T-cell population of cattle were studied. The results indicate that CD8(+) T-cells could be divided into γ/δ TCR1(+) and γ/δ TCR1(-) according to their expression of the γ/δ T-cell receptor.

Octahedral tilting in cation-ordered Jahn-Teller distorted perovskites--a group-theoretical analysis.

Computer-based group-theoretical methods are used to enumerate structures arising in A(2)BB'X(6) perovskites, with either rock-salt or checkerboard ordering of the B and B' cations, under the additional assumption that one of these two cations is Jahn-Teller active and thereby induces a distortion of the BX(6) (or B'X(6)) octahedron. The requirement to match the pattern of Jahn-Teller distortions to the cation ordering implies that the corresponding irreducible representations should be associated with the same point in the Brillouin zone. Effects of BX(6) (and B'X(6)) octahedral tilting are included in the usual way.

High-pressure crystallography of rhombohedral PrAlO(3) perovskite.

The evolution of the crystal structure of rhombohedral PrAlO(3) perovskite with pressure has been investigated by single-crystal x-ray diffraction and Raman scattering experiments. The structural evolution as indicated by lattice strains, octahedral tilts, and the distortions of the octahedral AlO(6) and polyhedral PrO(12) groups with increasing pressure, is controlled by the relative compressibilities of the AlO(6) octahedra and the PrO(12) site. Because the AlO(6) octahedra are more compressible than the PrO(12) sites, up to 7.

Crystal structures and phase transition in (Sr(0.8)Ce(0.2))(Mn(1-y)Co(y))O(3) (y = 0 and 0.2): the influence of Jahn-Teller distortion.

We have studied the crystal structures of (Sr(0.8)Ce(0.2))(Mn(1-y)Co(y))O(3) (y = 0 and 0.

Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn-Teller transitions in ABX3 perovskites. II. Application.

The structural evolution of selected perovskites containing Jahn-Teller cations has been investigated in the light of a formal analysis of symmetry hierarchies for phase transitions driven by octahedral tilting and Jahn-Teller cooperative distortions. General expressions derived from the strain/order-parameter coupling relationships allowed by symmetry are combined with observed changes in lattice parameters to reveal details of order-parameter evolution and coupling. LuVO3, YbVO3, YVO3 and CeVO3 are representative of systems which develop Jahn-Teller ordering schemes associated with irreducible representations M2+ and R3+ of the space group Pm3m.

Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn-Teller transitions in ABX3 perovskites. I. Theory.

Space groups, order-parameter and strain/order-parameter coupling relationships in ABX3 perovskite structures which combine cooperative Jahn-Teller distortions and octahedral tilting have been investigated from the perspective of group theory using the computer program ISOTROPY. Two common Jahn-Teller ordering schemes are associated with the irreducible representations M2+ and R3+ of the space group Pm3m. A third, less-common ordering scheme is associated with Gamma3+.

The antigen-specific memory CD8+ T-cell response induced by BCG in cattle resides in the CD8+gamma/deltaTCR-CD45RO+ T-cell population.

Tuberculosis (TB) remains a worldwide leading cause of death among infectious diseases. Development of safer and more efficacious vaccines requires a basic understanding of the protective mechanisms induced by BCG. Here we show that vaccination of cattle with BCG induces CD8+gamma/deltaTCR-CD45RO+ T-cells that can produce IFN-gamma, up-regulate transcription and expression of perforin, lyse BCG-infected monocyte-derived macrophages (MoMvarphi) and contribute to a reduction in the number of intracellular mycobacteria.

Spectroscopic studies of dehydrogenation of ammonia borane in carbon cryogel.

Ammonia borane (AB) is of great interest for storing hydrogen, an important issue in the growing field of hydrogen technology. The reaction pathways leading to the thermal decomposition of solid-state AB incorporated in carbon cryogels (CC) have been studied by spectroscopic methods. The time-dependent thermal decomposition was followed by in situ 11B nuclear magnetic resonance (NMR) and showed a significant increase in hydrogen release kinetics for AB in CC compared to neat AB.

The nucleation and growth of calcium phosphate by amelogenin.

The nucleation processes involved in calcium phosphate formation in tooth enamel are not well understood but are believed to involve proteins in the extracellular matrix. The ability of one enamel protein, amelogenin, to promote the nucleation and growth of calcium phosphate was studied in an in vitro system involving metastable supersaturated solutions. It was found that recombinant amelogenin (rM179 and rp(H)M180) promoted the nucleation of calcium phosphate compared to solutions without protein.

Workshop cluster 1+ gammadelta T-cell receptor T cells from calves express high levels of interferon-gamma in response to stimulation with interleukin-12 and -18.

Gammadelta T-cell receptor(+) T lymphocytes are an important element of the innate immune system. Early production of interferon (IFN)-gamma by gammadelta T cells may have a role in linking innate and adaptive immune responses and contribute to T helper-1 bias. We investigated the role of cytokines in the activation and induction of IFN-gamma secretion by bovine workshop cluster 1(+) (WC1(+)) gammadelta T cells.

Structures and phase transitions in the ordered double perovskites Ba2BiIIIBiVO6 and Ba2BiIIISbVO6.

High-resolution neutron powder diffraction has been used to investigate the structures and phase transitions in the double perovskites Ba(2)Bi(3+)Bi(5+)O(6) (dibarium dibismuth hexaoxide) and Ba(2)BiSbO(6) (dibarium bismuth antimony hexaoxide) in the temperature ranges 4.2-973 and 4.2-625 K, respectively.