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This study focuses on the effect of structure compression and cooling on the stereoelectronic properties of the planar π-conjugated TTF-BTD (TTF = tetrathiafulvalene; BTD = 2,1,3-benzothiadiazole) molecule, a prototypical example in which an electron-donor moiety is compactly annulated to an electron-acceptor moiety. Its partially oxidised iodine salt (TTF-BTD)2I3 is a crystalline semiconductor featuring segregated columns of TTF+0.5 units stacked via alternating short and long π–π interactions. We studied TTF-BTD at temperatures ranging from 300 K to 90 K and at pressures up to 7.5 GPa, using both X-ray diffraction and Raman spectroscopy to determine the properties of the compressed samples. Periodic DFT calculations and several theoretical tools were employed to characterize the calculated structural modifications and to predict the structural changes up to 60 GPa. The existence of an unprecedented new phase is predicted above 20 GPa, following a covalent bond formation between two neighbouring TTF-BTD units. [ABSTRACT FROM AUTHOR]

Volume crystallization of quartz, triggered by adding P2O5, was investigated in the multicomponent SiO2–Li2O–K2O–MgO–CaO–Al2O3–P2O5 glass system. Glass‐ceramics comprising quartz as the main crystal phase besides lithium disilicate (Li2Si2O5) as a minor crystal phase were produced by controlled crystallization from the parent glass. According to quantitative crystal phase analysis by means of Rietveld refinement the mass fraction of the minor Li2Si2O5 phase decreased with increasing P2O5 content, while the fraction of quartz increased. Scanning electron microscopy revealed lath‐like Li2Si2O5 embedded in a matrix of rather globular quartz crystals forming an interlocking microstructure. Well machinable glass‐ceramics with a mean biaxial flexural strength of about 300 MPa and a fracture toughness of about 2.0 MPa × m0.5 could be realized. With mean values ≥13.6 × 10−6 K−1 the glass‐ceramics coefficient of thermal expansion is close to the one reported for low‐quartz crystals. The ease of production based on conventional glass melting and fabrication technology together with the good mechanical, optical, and machining properties enables the application of these materials in prosthodontics. [ABSTRACT FROM AUTHOR]

The mechanical and optical properties of Li2Si2O5 glass-ceramics can be precisely controlled via the crystal morphology and content. However, the materials' coefficient of thermal expansion (CTE) depends on the fraction as well as the CTE of Li2Si2O5 and the residual glass phase, and therefore covers a rather narrow range between 10.2 and 11.3 *10−6 K−1 (100-400°C). This study presents a way to tailor the CTE of lithium disilicate-based glass-ceramics by controlled twofold precipitation of Li2Si2O5 and CsAlSi5O12 as a minor crystal phase with high CTE from homogenous Cs2O comprising bulk base glasses. The Cs2O content in the base glass significantly influences the nucleation and crystallization process of Li2Si2O5 as well as the microstructure of the glass-ceramic materials. While the precipitation of Li2SiO3 and Li2Si2O5 starts at temperatures ≤700°C, CsAlSi5O12 forms in parallel to the enhanced formation of Li2Si2O5 as a result of Li2SiO3 dissolution at crystallization temperatures >850°C. Glass-ceramics with a CTE ranging from 11 to 13.1*10−6 K−1 (25-500°C) and a mean biaxial strength ≥370 MPa were produced. The preliminary study of this glass system proofs the potential of twofold crystallization to control the CTE of lithium disilicate glass-ceramics. [ABSTRACT FROM AUTHOR]

The mechanical and optical properties of Li2Si2O5 glass-ceramics can be precisely controlled via the crystal morphology and content. However, the materials' coefficient of thermal expansion (CTE) depends on the fraction as well as the CTE of Li2Si2O5 and the residual glass phase, and therefore covers a rather narrow range between 10.2 and 11.3 *10−6 K−1 (100-400°C). This study presents a way to tailor the CTE of lithium disilicate-based glass-ceramics by controlled twofold precipitation of Li2Si2O5 and CsAlSi5O12 as a minor crystal phase with high CTE from homogenous Cs2O comprising bulk base glasses. The Cs2O content in the base glass significantly influences the nucleation and crystallization process of Li2Si2O5 as well as the microstructure of the glass-ceramic materials. While the precipitation of Li2SiO3 and Li2Si2O5 starts at temperatures ≤700°C, CsAlSi5O12 forms in parallel to the enhanced formation of Li2Si2O5 as a result of Li2SiO3 dissolution at crystallization temperatures >850°C. Glass-ceramics with a CTE ranging from 11 to 13.1*10−6 K−1 (25-500°C) and a mean biaxial strength ≥370 MPa were produced. The preliminary study of this glass system proofs the potential of twofold crystallization to control the CTE of lithium disilicate glass-ceramics. [ABSTRACT FROM AUTHOR]

Phase stability, elastic behavior, and pressure-induced structural evolution of synthetic boron-mullite Al5 BO9 ( a = 5.6780(7), b = 15.035(6), and c =7.698(3) Å, space group Cmc21, Z = 4) were investigated up to 25.6(1) GPa by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell (DAC) under hydrostatic conditions. No evidence of phase transition was observed up to 21.7(1) GPa. At 25.6(1) GPa, the refined unit-cell parameters deviated significantly from the compressional trend, and the diffraction peaks appeared broader than at lower pressure. At 26.7(1) GPa, the diffraction pattern was not indexable, suggesting amorphization of the material or a phase transition to a high-pressure polymorph. Fitting the P-V data up to 21.7(1) GPa with a second-order Birch-Murnaghan Equation-of-State, we obtained a bulk modulus KT0 = 164(1) GPa. The axial compressibilities, here described as linearized bulk moduli, are as follows: KT0( a) = 244(9), KT0( b) = 120(4), and KT0( c) = 166(11) GPa ( KT0( a): KT0( b): KT0( c) = 2.03:1:1.38). The structure refinements allowed a description of the main deformation mechanisms in response to the applied pressure. The stiffer crystallographic direction appears to be controlled by the infinite chains of edge-sharing octahedra running along [100], making the structure less compressible along the a-axis than along the b- and c-axis. [ABSTRACT FROM AUTHOR]

The zeolite mineral goosecreekite CaAl2Si6O16⋅5H2O has been structurally investigated between 25 and 600 °C to monitor structural modifications upon partial dehydration. Temperature-dependent in situ powder and single-crystal X-ray techniques were combined with TG/DTA experiments. Goosecreekite has a porous framework structure with well-ordered Si,Al distribution. In its natural form extraframework Ca is seven-coordinated. Up to ca. 100 °C, 1 H2O molecule is expelled reducing the Ca coordination from 7 to 6 accompanied by very minor changes of the tetrahedral framework. Depending on humidity and equilibration time a second structural change begins between 150 and 250 °C due to loss of additional 2.8 H2O pfu. The space group P21 is maintained but the c axis doubles and the structure is highly twinned. This new phase may be interpreted with a disordered model having two different framework topologies: one with the original T-O-T linkage and a second one with broken T-O-T links. Starting at ca. 300 °C, another 1.2 H2O are lost and this new orthorhombic, strongly contracted phase of P212121 symmetry has five-coordinated Ca. The X-ray powder signal of the orthorhombic phase persists up to 600 °C, but the structure becomes increasingly X-ray amorphous until complete destruction at 675 °C. A single crystal (P21 phase with doubled c axis) partly dehydrated at 200 °C recovers the structure of natural goosecreekite under ambient conditions. Similar rehydration occurs after one month under ambient humidity for a powder sample of the orthorhombic P212121 phase produced by heating of goosecreekite to 325 °C. [ABSTRACT FROM AUTHOR]

Abstract: Orthorhombic Al2O3-rich aluminoborate is an important ceramic material for which two slightly different compositions have been assumed: Al5BO9 (5Al2O3:B2O3) and Al18B4O33 (9Al2O3:2B2O3). The formula Al18B4O33 (=Al4.91B1.09O9) was derived from results of chemical analyses when crystal structure data were not yet available. Subsequent structural investigations indicated Al5BO9 composition. Nevertheless, Al18B4O33 was still accepted as the correct stoichiometry assuming that additional B replaces 9% Al. Powder samples of both compositions and ones with excess boron were prepared by solid state reactions between α-Al2O3 and B2O3/H3BO3 at temperatures above 1100°C and single-crystals were grown from flux at 1100 and 1550°C. Products were investigated by single-crystal and powder XRD, 11B and 27Al solid-state MAS-NMR, Raman and FTIR spectroscopy as well as Laser-ablation ICP-MS. No indication of the predicted 9% B→Al substitution was found. LA ICP-MS indicated 12.36(27)wt% B2O3 corresponding to Al4.97B1.03O9. Hence, the suggested Al18B4O33 stoichiometry can be excluded for all synthesized samples. A very low amount of Al vacancies at a five-fold coordinated site are likely, charge balanced by an additional nearby three-fold coordinated B site. All evidences indicate that the title compound should be reported as Al5−x B1+x O9 with x<0.038(6), which is close to Al5BO9. [ABSTRACT FROM AUTHOR]

Abstract: CsAlSi5O12 crystals were synthesized at high temperature by slow cooling of a vanadium oxide flux. Single-crystal X-ray diffraction structure analysis and electron microprobe analyses yielded the microporous CAS zeolite framework structure of Cs0.85Al0.85Si5.15O12 composition. High-temperature single-crystal and powder X-ray diffraction studies were utilized to analyze anisotropic thermal expansion. Rietveld refined cell constants from powder diffraction data, measured in steps of 25°C up to 700°C, show a significant decrease in expansion above 500°C. At 500°C, a displacive, static disorder–dynamic disorder-type phase transition from the acentric low-temperature space group Ama2 to centrosymmetric Amam (Cmcm in standard setting) was found. Thermal expansion below the phase transition is governed by rigid-body TO4 rotations accompanied by stretching of T–O–T angles. Above the phase transition at 500°C all atoms, except one oxygen (O6), are fixed on mirror planes. Temperature-dependent polarized Raman single-crystal spectra between −270 and 300°C and unpolarized spectra between room temperature and 1000°C become increasingly less resolved with rising temperature confirming the disordered static–disordered dynamic type of the phase transition. [Copyright &y& Elsevier]

Through the combined efforts of the educational and health care professionals, in a hospital based outpatient special class, a unique environment was provided for children with learning disabilities. Eight children who were uncontainable in public schools showed improvement after four semesters in this special class. Procedures emphasized daily intercommunication between educators and staff, enabling modification in progress to be made constantly. Drugs were used to help these children be more receptive to learning. We have found both Ritalin and Dexedrine decreased distractibility, irritability, silly behavior, and overactivity. [ABSTRACT FROM AUTHOR]

The article presents a study on the intellectual development of children with cerebral palsy as a factor in therapeutic progress. The authors describe a survey made on children with cerebral palsy from the Cerebral Palsy Clinic at the Long Island College Hospital and the Cerebral Palsy School Unit at P. S. 67 in Brooklyn, New York. Data on birth history, psychological test results, maturational status, functional capacity, and progress in the varied therapeutic areas are collected.