Luminescent mechanochromism has been intensively studied in the past few years. However, the difference in the anisotropic grinding and the isotropic compression is not clearly distinguished in many cases, in spite of the importance of this discrimination for the application of such mechanochromic materials. We now report the distinct luminescent responses of a new organic fluorophore, tetrathiazolylthiophene, to these stresses. The multichromism is achieved over the entire visible region using the single fluorophore. The different mechanisms of a blue shift by grinding crystals and of a red shift under hydrostatic pressure are fully investigated, which includes a high-pressure single-crystal X-ray diffraction analysis. The anisotropic and isotropic modes of mechanical loading suppress and enhance the excimer formation, respectively, in the 3D hydrogen-bond network.

Here we report on the finding of pure boron nitride (BN) nanotubes that do not contain any additional inclusions and on a new method for their growth: laser heating of boron nitrides at high nitrogen pressure (5–15 GPa). The multiwalled nanotubes were observed using high resolution electron microscopy and were chemically characterized by electron energy loss spectroscopy. The circular or polygonal cross-sectional nanotubes, which have 3–8 shells and a characteristic outer dimension cross section of 3–15 nm, were found to have grown either in melted cubic BN or in hexagonal+amorphous BN that had recrystallized on the specimen’s surface from the fluid phase.

The structural and electronic properties of BiCoO(3) under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO(3) type to a centrosymmetric GdFeO(3) type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure-temperature phase diagram of BiCoO(3) has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.

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High-pressure structural properties of multiferroic perovskite-type BiFeO 3 have been investigated by high-resolution synchrotron X-ray powder diffraction at room temperature up to 9.7 GPa. BiFeO 3 shows rather complicated structural behavior. The ambient-pressure ferroelectric R3c phase transforms to an orthorhombic phase OI at around 4 GPa during compression. The OI phase is characterized by a superstructure √ 2a p Â3 √ 2a p Âa p , where a p is the parameter of the cubic perovskite subcell (a=5.4939(4) A ˚, b=16.6896(9) A ˚, c=3.8728(2) A ˚at 4.9 GPa). The OI phase transforms to an orthorhombic phase OII at around 7 GPa. The OII phase is characterized by a superstructure √ 2a p  3 √ 2a p  2a p (a = 5.5021(3) A ˚, b = 16.2439(11) A ˚, c = 7.6960(4) A ˚at 9.7 GPa). During decompression, significant hysteretic behavior was found. The OII phase was stable down to about 3 GPa. The OII phase then transforms to an orthorhombic phase OIII that is characterized by a superstructure √ 2a p  2 √ 2a p  2a p (a = 5.5617(6) A ˚, b = 11.2153(10) A ˚, c = 7.7788(7) A ˚at 2.2 GPa). The R3c phase appeared below about 1 GPa; however, even at ambient pressure, traces of the OIII phase remained. The OIII phase seems to be isostructural with antiferroelectric PbZrO 3 (space group Pbam).