Structural Disorder in (Bi, M)₂(Fe, Mn, Bi)₂O_6+<i>x</i> (M = Na or K) Pyrochlores Seen from Reverse Monte Carlo Analysis of Neutron Total Scattering

The average structures of the polycrystalline pyrochlores (Na_0.60Bi_1.40)­(Fe_1.06Mn_0.17Bi_0.77)­O_6.87 and (K_0.24Bi_1.51)­(Fe_1.07Mn_0.15Bi_0.78)­O_6.86 can be refined through Rietveld refinement against Bragg scattering data using cubic space group <i>Fd</i>3̅<i>m</i>, with off-centered 96<i>h</i> and 32<i>e</i> positions describing the A₂O′ network. Investigation of their local structures through neutron total scattering confirms the extent of disorder within these materials, and furthermore shows significant deviation from the average structure, which is not accounted for through analysis of Bragg data alone. Reverse Monte Carlo (RMC) analysis with a 6 × 6 × 6 supercell was used to model accurately this local disorder, revealing ellipsoidal distributions for A-site potassium, distinctly different from the hollow torus-shaped distributions for the sodium and bismuth cations. It is shown through bond valence sum analysis that while these atomic displacements allow for the steric preferences of Bi³⁺, they are also necessary to satisfy the valence of both the bismuth and the alkali metals on the A sites. Analysis of the final RMC configuration showed the BO₆ octahedra for the separate B site metals to be more regular (O–B–O ≈ 90°) than those in the Rietveld model (O–B–O ≈ 85/95°) which describes an average of the three different environments

Metastable (Bi, M)₂(Fe, Mn, Bi)₂O_6+<i>x</i> (M = Na or K) Pyrochlores from Hydrothermal Synthesis

The hydrothermal syntheses, structures, and magnetism of two new pyrochlore oxides of compositions (Na_0.60Bi_1.40)­(Fe_1.06Mn_0.17Bi_0.77)­O_6.87 and (K_0.24Bi_1.51)­(Fe_1.07Mn_0.15Bi_0.78)­O_6.86 are described. With preparation at 200 °C for 6 h in solutions of sodium or potassium hydroxide, the alkali metals introduced from these mineralizers are essential to the synthesis of the phases. The average long-range order of the pyrochlore structure, with space group <i>Fd</i>3̅<i>m</i>, was investigated and refined against X-ray and neutron diffraction data, and it was shown that disorder is present in both the metal and coordinating oxygen positions, along with metal-mixing across both the A and B sites of the structure. XANES analysis confirms the presence of Mn⁴⁺, mixed valence Bi³⁺ and Bi⁵⁺, and Fe³⁺, the last also verified by ⁵⁷Fe Mössbauer spectroscopy. Magnetic measurements show a lack of long-range magnetic ordering that is typical of geometrically frustrated pyrochlores. The observed glasslike interactions occur at low temperatures, with the onset temperature depending upon the magnitude of the applied external field. Variable temperature X-ray diffraction shows that these pyrochlores are metastable and collapse on heating at ca. 395 °C, which suggests that their formation by conventional solid-state synthesis would be impossible

Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution La_<i>x</i>Sm_1–<i>x</i>CrO₃

A new mixed rare-earth orthochromite series, La_<i>x</i>Sm_1–<i>x</i>CrO₃, prepared through single-step hydrothermal synthesis is reported. Solid solutions (<i>x</i> = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370 °C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group <i>Pnma</i> over the full composition range. Unit cell volumes and Cr–O–Cr bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm^–1 is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr³⁺ spins with weak ferromagnetic component at Néel temperatures (<i>T</i>_N) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr³⁺ and Sm³⁺ ions are examined with enhanced susceptibilities below <i>T</i>_N due to polarization of Sm³⁺ moments. At low temperatures the Cr³⁺ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility

Optimising motor learning in infants at high risk of cerebral palsy: a pilot study

Background: The average age for the diagnosis of cerebral palsy (CP) is 19 months. Recent neuroplasticity literature suggests that intensive, task-specific intervention ought to commence as early as possible and in an enriched environment, during the critical period of neural development. Active motor interventions are effective in some populations, however the effects of active motor interventions on the motor outcomes of infants with CP have not been researched thoroughly, but pilot work is promising. The aim of this study was to determine the short- term effects of “GAME”; a new and novel goal-oriented activity-based, environmental enrichment therapy programme on the motor development of infants at high risk of CP and test study procedures for a randomized controlled trial (RCT). Methods: Pragmatic 2-group pilot RCT to assess motor outcomes, goal attainment, parent well-being and home environment quality, after 12-weeks of GAME intervention versus standard care. GAME included: creation of movement environments to elicit motor behaviours; parent training in motor learning and task analysis; frequent practice of motor tasks using a programme that was individualised to the child, was varied and focused on self-initiated movement. Data were analyzed using multiple regression. Results: Thirteen infants were consented, randomised, treated and completed the study. At study conclusion, the GAME group (n = 6) demonstrated an advantage in Total Motor Quotient of 8.05 points on the Peabody Developmental Motor Scale-2 (PDMS-2) compared to the standard care group (n = 7) (p \u3c .001). No significant differences existed between groups on any other measure. Conclusions: GAME appears to offer a promising and feasible new motor intervention for CP, with favourable short-term motor outcomes. A pressing need exists for an adequately powered RCT with long-term end points, to determine if GAME may advance these children’s motor trajectory

Control of Ionic Conductivity by Lithium Distribution in Cubic Oxide Argyrodites Li_6+<i>x</i>P_1–<i>x</i>Si_<i>x</i>O₅Cl

Argyrodite is a key structure type for ion-transporting materials. Oxide argyrodites are largely unexplored despite sulfide argyrodites being a leading family of solid-state lithium-ion conductors, in which the control of lithium distribution over a wide range of available sites strongly influences the conductivity. We present a new cubic Li-rich (>6 Li+ per formula unit) oxide argyrodite Li7SiO5Cl that crystallizes with an ordered cubic (P213) structure at room temperature, undergoing a transition at 473 K to a Li+ site disordered F4̅3m structure, consistent with the symmetry adopted by superionic sulfide argyrodites. Four different Li+ sites are occupied in Li7SiO5Cl (T5, T5a, T3, and T4), the combination of which is previously unreported for Li-containing argyrodites. The disordered F4̅3m structure is stabilized to room temperature via substitution of Si4+ with P5+ in Li6+xP1–xSixO5Cl (0.3 x < 0.85) solid solution. The resulting delocalization of Li+ sites leads to a maximum ionic conductivity of 1.82(1) × 10–6 S cm–1 at x = 0.75, which is 3 orders of magnitude higher than the conductivities reported previously for oxide argyrodites. The variation of ionic conductivity with composition in Li6+xP1–xSixO5Cl is directly connected to structural changes occurring within the Li+ sublattice. These materials present superior atmospheric stability over analogous sulfide argyrodites and are stable against Li metal. The ability to control the ionic conductivity through structure and composition emphasizes the advances that can be made with further research in the open field of oxide argyrodites