Arsenic-Containing Chalcophosphate Molecular Anions

Panoramic Synthesis as an Effective Materials Discovery Tool: The System Cs/Sn/P/Se as a Test Case

The common approach to the synthesis of a new material involves reactions held at high temperatures under certain conditions such as heating in a robust vessel in the dark for a period until it is judged to have concluded. Analysis of the vessel contents afterward provides knowledge of the final products only. Intermediates that may form during the reaction process remain unknown. This lack of awareness of transient intermediates represents lost opportunities for discovering materials or understanding how the final products form. Here we present new results using an emerging in situ monitoring approach that shows high potential in discovering new compounds. In situ synchrotron X-ray diffraction studies were conducted in the Cs/Sn/P/Se system. Powder mixtures of Cs₂Se₂, Sn, and PSe₂ were heated to 650 °C and then cooled to room temperature while acquiring consecutive in situ synchrotron diffraction patterns from the beginning to the end of the reaction process. The diffraction data was translated into the relationship of phases present versus temperature. Seven known crystalline phases were observed to form on warming in the experiment: Sn, Cs₂Se₃, Cs₄Se₁₆, Cs₂Se₅, Cs₂Sn₂Se₆, Cs₄P₂Se₉, and Cs₂P₂Se₈. Six unknown phases were also detected; using the in situ synchrotron data as a guide three of them were isolated and characterized ex situ. These are Cs₄Sn(P₂Se₆)₂, α-Cs₂SnP₂Se₆, and Cs₄(Sn₃Se₈)[Sn(P₂Se₆)]₂. Cs₄(Sn₃Se₈)[Sn(P₂Se₆)]₂ is a two-dimensional compound that behaves as an n-type doped semiconductor below 50 K and acts more like a semimetal at higher temperatures. Because all crystalline phases are revealed during the reaction, we call this approach "panoramic synthesis".

Scandium Selenophosphates: Structure and Properties of K4Sc2(PSe4)2(P2Se6)

The new compound K4Sc2P4Se14 was synthesized via the polychalcogenide flux method. It crystallizes in the space group C2/c, and the structure is composed of (1)/∞[Sc2P4Se14(4-)] chains that are separated by K(+) cations. The structural motif features two [PSe4](3-) units and one [P2Se6](4-) unit bridging the Sc centers and has not been reported for any other compound. The (1)/∞[Sc2P4Se14(4-)] chains pack in a crosshatched pattern perpendicular to the c axis of the crystal, forming channels for half of the K(+) atoms while the other half occupy empty space between the chains. The orange-yellow crystals of K4Sc2P4Se14 are air-sensitive and gradually turn red over the course of a couple hours. The band gap of the phase is 2.25(2) eV, and Raman spectroscopy shows the symmetric stretches of the selenophosphate groups to be at 231 and 216 cm(-1) for the [PSe4](3-) and [P2Se6](4-) units, respectively. Solid-state (31)P MAS NMR of K4Sc2P4Se14 shows two prominent peaks at 11.31 and -23.07 ppm and one minor peak at -106.36 ppm, most likely due to degradation of the product or an unknown second phase.

Surfactant-thermal method to synthesize a novel two-dimensional oxochalcogenide

A new two-dimensional (2D) oxosulfide, (N2H4)2Mn3Sb4S8(μ3-OH)2 (1), has been successfully synthesized under surfactant-thermal conditions with hexadecyltributylphosphonium bromide as the surfactant. Compound 1 has a layered structure and contains a novel [Mn3(μ3-OH)2]n chain along the b-axis. The photocatalytic activity for compound 1 has been demonstrated under visible-light irradiation and continuous H2 evolution was observed. Our results indicate that surfactant-thermal synthesis could be a promising method for growing novel crystalline oxochalcogenides with interesting structures and properties.

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.