J. Appl. Cryst.の発刊に際して

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Hybrid porous solids: past, present, future

We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

The aim of this critical review is to provide a broad but digestible overview of mechanochemical synthesis, i.e. reactions conducted by grinding solid reactants together with no or minimal solvent. Although mechanochemistry has historically been a sideline approach to synthesis it may soon move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous, and because of the opportunities it provides for developing more sustainable methods. Concentrating on recent advances, this article covers industrial aspects, inorganic materials, organic synthesis, cocrystallisation, pharmaceutical aspects, metal complexes (including metal–organic frameworks), supramolecular aspects and characterization methods. The historical development, mechanistic aspects, limitations and opportunities are also discussed (314 references).

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Mechanochemistry: opportunities for new and cleaner synthesis

We performed optical‐absorption studies of the energy gap in various GaN samples in the temperature range from 10 up to 600 K. We investigated both bulk single crystals of GaN and an epitaxial layer grown on a sapphire substrate. The observed positions of the absorption edge vary for different samples of GaN (from 3.45 to 3.6 eV at T=20 K). We attribute this effect to different free‐electron concentrations (Burstein–Moss effect) characterizing the employed samples. For the sample for which the Burstein shift is zero (low free‐electron concentration) we could deduce the value of the energy gap as equal to 3.427 eV at 20 K. Samples with a different free‐electron concentration exhibit differences in the temperature dependence of the absorption edge. We explain the origin of these differences by the temperature dependence of the Burstein–Moss effect.

Temperature dependence of the energy gap in GaN bulk single crystals and epitaxial layer

We report the synthesis, crystal structure, thermal, dielectric, IR, and Raman studies of [NH4][Mg(HCOO)3] formate. Single-crystal X-ray diffraction shows that it crystallizes in the hexagonal space group P6322, with orientationally disordered NH4+ ions located in the cages of the network. Upon cooling, [NH4][Mg(HCOO)3] undergoes a phase transition at around 255 K to the ferroelectric P63 structure. Raman and IR spectra show a strong increase in intensity of the N–H stretching bands as well as narrowing of the bands related to the NH4+ ions upon cooling. These changes indicate that the phase transition is due to orientational ordering of the NH4+ ions. Analysis of the Raman data show, however, that the rotational and translational motions of NH4+ do not freeze completely at the phase transition but exhibit further slowing down below 255 K, and the motional freezing becomes nearly complete below 140 K.

Structure, phonon properties, and order-disorder transition in the metal formate framework of [NH4][Mg(HCOO)3].

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Crystal structure of Cu2Se

Pentakis (imidazolium) undecachlorodibismuthate(III), ${({\mathrm{C}}_{3}{\mathrm{N}}_{2}{\mathrm{H}}_{5})}_{5}{\mathrm{Bi}}_{2}{\mathrm{Cl}}_{11}$, has been synthesized and studied by means of the x-ray, differential scanning calorimetry (DSC), and dielectric methods over a wide temperature range. The room temperature crystal structure has been determined as monoclinic, space group $P{2}_{1}∕n$ with $a=13.616\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $b=14.684\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $c=9.045\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and $\ensuremath{\beta}=96.85\ifmmode^\circ\else\textdegree\fi{}$. Two solid--solid phase transitions: $P\overline{4}n2\stackrel{360\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}∕n$ $(I\ensuremath{\rightarrow}II)$, and $P{2}_{1}∕n\stackrel{166\phantom{\rule{0.3em}{0ex}}\mathrm{K}}{\ensuremath{\rightarrow}}P{2}_{1}$ $(II\ensuremath{\rightarrow}III)$, discontinuous and continuous in nature, respectively, have been revealed. The dielectric and pyroelectric measurements allow us to characterize the lowest temperature phase (III) as ferroelectric with the Curie point at $166\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and saturated spontaneous polarization value of the order of $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\mathrm{C}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$ along the $\mathbit{b}$ axis. The ferroelectric phase transition mechanism is governed by the dynamics of imidazolium cations. The room temperature, paraelectric phase (II) demonstrates additionally the ferroelastic properties.

Structure and ferroelectric properties of ( C 3 N 2 H 5 ) 5 Bi 2 Cl 11

Bismuth ferrite nanopowders have been obtained by mechanochemical synthesis. The materials were characterized by high resolution electron microscopy, X-ray diffraction and NIR Raman scattering. The XRD pattern of the powder consists of reflections, characteristic of BiFeO 3 perovskite structure, superimposed on broad maxima that can be ascribed to an amorphous/disordered phase. The analysis of the two broad bands at low 2 θ angle yields mean distances of about 3 and 1.8 A which may be related to Bi O and Fe O bonds, respectively. The powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm. The grains of sizes larger than about 30 nm exhibit well-developed crystalline structure.

Adam Pietraszko

Papers

Temperature dependence of the energy gap in GaN bulk single crystals and epitaxial layer

Structure, phonon properties, and order-disorder transition in the metal formate framework of [NH4][Mg(HCOO)3].

Crystal structure of Cu2Se

Structure and ferroelectric properties of ( C 3 N 2 H 5 ) 5 Bi 2 Cl 11

Characterization of BiFeO3 nanopowder obtained by mechanochemical synthesis