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Metal phthalocyanines, which are examples of one-dimensional semiconductors, are widely used as active layers of chemiresistive sensors for detecting various gases, in particular ammonia. Despite the high interest in such sensors, there have been few systematic studies on the effect of the type of substituent and structural features of films on their chemiresistive response to gases. In this work, films of zinc phthalocyanine (ZnPc-1, 2, 3 and 4) bearing alkylthio (–S(CH2)5CH3) and polyoxo (–O(CH2CH2O)3CH3 and –S(CH2CH2O)3CH3) substituents, which exhibit liquid crystalline properties and, as a consequence, are capable of forming ordered films, were tested as active layers of chemiresistive sensors for the detection of low concentrations of ammonia (0.1–50 ppm). The effect of the type of substituent on the films' alignment and sensor response to ammonia was studied for the first time. It was shown that the films of all investigated zinc phthalocyanines demonstrated a reversible chemiresistive sensor response to gaseous ammonia. The sensor response of the as-deposited films of ZnPc-1 and ZnPc-2 with polyoxo-substituents, which are liquid crystalline at room temperature, was noticeably higher than that of ZnPc-3 and ZnPc-4, which form polycrystalline disordered films. The limit of ammonia detection was 17 ppb for ZnPc-1 and ZnPc-2 films. Heat treatment of ZnPc-1 and ZnPc-2 films did not cause any changes in their structure and sensor properties, while ZnPc-3 and ZnPc-4 films became more ordered after heating, and their sensor response increased several times. This led to a reduction in the detection limit of ammonia to 10 ppb in the case of the ZnPc-3 film. All investigated films have high selectivity to ammonia in the presence of carbon dioxide and vapors of some volatile organic compounds. [ABSTRACT FROM AUTHOR]

The Fe–C system, which is widely used to grow commercial high‐pressure–high‐temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single‐crystal and powder X‐ray diffraction, as well as electron probe micro‐analysis and scanning electron microscopy. The experiments were performed using a multiple‐anvil high‐pressure apparatus of 'split‐sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe–C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12−x. Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12−x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal–carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide. [ABSTRACT FROM AUTHOR]

The co-crystallisation of [NiEn3](NO3)2 (En = ethylenediamine) with Na2MoO4 and Na2WO4 from a water solution results in the formation of [NiEn3](MoO4)0.5(WO4)0.5 co-crystals. According to the X-ray diffraction analysis of eight single crystals, the parameters of the hexagonal unit cell (space group P–31c, Z = 2) vary in the following intervals: a = 9.2332(3)–9.2566(6); c = 9.9512(12)–9.9753(7) Å with the Mo/W ratio changing from 0.513(3)/0.487(3) to 0.078(4)/0.895(9). The thermal decomposition of [NiEn3](MoO4)0.5(WO4)0.5 individual crystals obtained by co-crystallisation was performed in He and H2 atmospheres. The ex situ X-ray study of thermal decomposition products shows the formation of nanocrystalline refractory alloys and carbide composites containing ternary Ni–Mo–W phases. The formation of carbon–nitride phases at certain stages of heating up to 1000 °C were shown. [ABSTRACT FROM AUTHOR]

In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR4-np, R = F, Cl) and peripheral (ZnPcR4-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor response to low concentration of ammonia is studied. The structure and morphology of the zinc phthalocyanines films (ZnPcR4) were investigated by X-ray diffraction and atomic force microscopy methods. To understand different effects of chlorine and fluorine substituents, the strength and nature of the bonding of ammonia and ZnPcHal4 molecules were studied by quantum chemical simulation. It was shown on the basis of comparative analysis that the sensor response to ammonia was found to increase in the order ZnPcCl4-np < ZnPcF4-np < ZnPcF4-p < ZnPcCl4-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH3 and halogen substituents in the phthalocyanine rings. ZnPcCl4-p films demonstrate the maximal sensor response to ammonia with the calculated detection limit of 0.01 ppm; however, they are more sensitive to humidity than ZnPcF4-p films. It was shown that both ZnPcF4-p and ZnPcCl4-p and can be used for the selective detection of NH3 in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol. [ABSTRACT FROM AUTHOR]

High-entropy alloys containing 5 and 6 platinum group metals have been prepared by thermal decomposition of single-source precursors non requiring high temperature or mechanical alloying. The prepared Ir 0.19 Os 0.22 Re 0.21 Rh 0.20 Ru 0.19 alloy is the first example of a single-phase hexagonal high-entropy alloy. Heat treatment up to 1500 K and compression up to 45 GPa do not result in phase changes, a record temperature and pressure stability for a single-phase high-entropy alloy. The alloys show pronounced electrocatalytic activity in methanol oxidation, which opens a route for the use of high-entropy alloys as materials for sustainable energy conversion. [ABSTRACT FROM AUTHOR]