Volume 80, Issue 6-7

A micro-electro-mechanical system (MEMS) gas sensor based on a Ni–In 2 O 3 /ZnO nano-composite for detecting hydrogen sulfide gas (H 2 S) was constructed. The sensitive nano-material is applied onto a hot plate to create a MEMS gas sensor. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were employed to examine the crystal structure, elemental composition, and surface morphology of the fabricated Ni–In 2 O 3 /ZnO gas composite film. The sensitive material has a dense porous surface morphology and is uniformly coating the MEMS device. The coating on the MEMS microheater exhibits high selectivity and a sensitivity of 3.4 ± 0.12 μA ppm −1 to H 2 S, maintaining strong linear behavior. Additionally, the response duration is 4.4 s, while the recovery period is 5.2 s. With superior responsiveness, precise targeting, stable performance, and repeatable outcomes, this device opens new avenues for creating cost-effective and high-performance solutions for future H 2 S sensing.

In this research, a novel microsensor specifically engineered for detecting hydrogen sulfide (H 2 S) gas is introduced. Through chemical precipitation, Co x Zn 1− x O ( x  = 0, 0.05, 0.1, 0.15, 0.2) materials with a flaky structure were produced, and the resulting composite film’s structural, compositional, and morphological properties were examined using XRD, XPS, and SEM analyses. The Co x Zn 1− x O material was confirmed through XRD and XPS analyses. SEM images demonstrated that the material exhibits a porous structure and forms a uniform layer across the microsensor device. Co 0.1 Zn 0.9 O demonstrated the best gas-sensing performance. When applied on the micro-hotplate, it shows strong sensitivity and selectivity. The results of the experiments revealed that the sensor’s sensitivity is 0.02565 mA ppm −1 (95 % confidence intervals, CI: 0.0255 to 0.0258), demonstrating strong linear correlation 0.99506 (95 % CI: 0.9986 to 0.9977), and offering quick response and recovery intervals between 7.9 s (95 % CI: 7.757 to 8.043) and 6.5 s (95 % CI: 6.357 to 6.643). This gas sensor offers broad application prospects in environmental H 2 S monitoring.

Polycrystalline materials with the compositions CaLa 2 Zn 1− x Ca x Ti 2 O 9 ( x  = 0.00, 0.15, 0.30, 0.45, 0.90 and 1.00) were synthesized via the conventional solid-state reaction method under ambient conditions. Their crystal structures were determined at room temperature from powder X-ray diffraction (XRPD) using the Rietveld method. For compositions with x  = 0.00, 0.15, 0.30, and 0.45, the structures crystallize in the orthorhombic space group Pbnm , with the octahedra tilting in-phase along the [001] direction, and out-of-phase along the [100] and [010] directions of the pseudocubic cell; corresponding to the tilt system a − a − c + . Compositions with x  = 0.90 and 1.00 adopt the monoclinic space group P 2 1 / n , with the octahedra tilting in-phase along the c axis and out-of-phase along the a and b axes, consistent with the tilt system a − b − c + . In both structural models, the frameworks consist of corner-sharing B O 6 octahedra in three dimensions. The structural distortion of the monoclinic phases indicates partial 1:1 B -site ordering between Ti 4+ (occupying the 2 c site) and a random mixture of 2/3 (Zn 2+ 1− x Ca 2+ x ) and 1/3 Ti 4+ (occupying the 2 d site). Along the c axis, the B –O1– B bond angles in the orthorhombic phases ( B  = Zn(Ca2)/Ti) were calculated to be 156.3° ( x  = 0.00), 157.3° ( x  = 0.15), 154.8° ( x  = 0.30), and 157.2° ( x  = 0.45). In contrast, the Ti1–O3– B ′ bond angles in the monoclinic phases ( B ′ = Zn(Ca2)/Ti2) were found to be 158.5° ( x  = 0.90) and 158.3° ( x  = 1.00). These materials could have promising potential for applications in electrical and dielectric devices.

Seven phases RE 10 Co 3 In 10 ( RE  = Y, Gd, Tb, Dy, Ho, Er, Tm) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T  = 870 K for 1,500 h in evacuated and sealed quartz ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The structure model of Tb 10 Co 3 In 10 was obtained by Direct Methods using a data set from an intergrown single crystal of known TbCo 2 In and the new phase Tb 10 Co 3 In 10 . The compound crystallizes in its own structure type (orthorhombic space group Pbam , Z  = 4; a  = 25.462(13); b  = 24.026(12); c  = 3.605(2) Å; V  = 2,205.0(2) Å 3 ) and belongs to a large family of two-layer structures (with layers perpendicular to the short unit cell axes) based on the intergrowth of AlB 2 - and CsCl-type related slabs. Tb 10 Co 3 In 10  – together with the structure types Tb 3 Ru 0.97 In 3 and Nd 39 Ir 10.98 In 36.02  – forms a homologous series RE m + n + q T 2 n X m +2 q , where m is the number of REX (CsCl type) slabs and n the number of RET 2 and q the number of REX 2 (both AlB 2 type) slabs ( T  = Co, Ru, Ir; X  = In). For Tb 10 Co 3 In 10 the values are m  = 28, n  = 6, q  = 6. The structure of the  RE 10 Co 3 In 10 compounds was refined from powder X-ray diffraction patterns using the F ullprof program package.

The interaction of components in the system DyNiIn-DyNiSn was studied by powder X-ray diffraction and scanning electron microscopy in the full concentration range at T  = 870 K. The limited solubility of the p -elements in the parent compounds of equiatomic composition with the formation of substitutional solid solutions with the following compositions was established: DyNiIn 1.0–0.5 Sn 0–0.5 (ZrNiAl-type structure; hexagonal space group P 6 ‾ $\overline{6}$ 2 m ; а =  0.74480(9)–0.74323(6); с  = 0.37811(5)–0.37635(4) nm) and DyNiSn 1.0–0.8 In 0–0.2 (TiNiSi-type structure; orthorhombic space group Pnma ; a =  0.711951(7)–0.71145(7); b =  0.44496(4)–0.44572(4); c =  0.76669(8)–0.76787(9) nm). Partial substitution of In by Sn atoms was confirmed by X-ray analysis of single crystals of the phases: DyNiIn 0.7 Sn 0.3 (ZrNiAl-type structure; hexagonal space group P 6 ‾ $\overline{6}$ 2 m ; hP 9, а  = 0.74454(7); с  = 0.37569(4) nm; V  = 0.18036(3) nm 3 ; R 1 = 0.0203; w R 2 = 0.0504) and DyNiIn 0.1 Sn 0.9 (TiNiSi-type structure; orthorhombic space group Pnma ; o P12, a  = 0.71086(2); b  = 0.44508(1); c  = 0.76560(2) nm; V  = 0.24223(1) nm 3 ; R 1 = 0.0233; w R 2 = 0.0579). The existence ranges within the solid solutions and their structural features are briefly discussed.

Metathesis reactions with Ag[C(CN) 3 ] and rare-earth metal trichlorides RE Cl 3 ( RE  = Sc, Y or La) in water yielded colorless single crystals of Sc[C(CN) 3 ] 3 (H 2 O) 3 (I) , Y[C(CN) 3 ] 3 (H 2 O) 2 (II) and La[C(CN) 3 ] 3 (H 2 O) 4 (III) . (I) crystallizes in the triclinic space group P 1 ‾ $\overline{1}$ (no. 2) with the lattice parameters a  = 964.73(7), b  = 1024.26(7), c  = 1096.48(8) pm, α  = 70.767(3), β  = 64.936(3), γ  = 62.481(3)°, Z  = 2; (II) adopts the orthorhombic space group P 2 1 2 1 2 1 (no. 19, a  = 1011.06(7), b  = 1172.54(8), c  = 1419.21(9) pm, Z  = 4), while (III) exhibits the monoclinic space group C 2/ c (no. 12, a  = 2843.17(19), b  = 789.74(5), c  = 1812.31(12) pm, β  = 106.938(3)°, Z  = 8). In (I) , a quasi-molecular dimer forms with C.N. (Sc 3+ ) = 7, (II) shows a rather complex framework with C.N. (Y 3+ ) = 8, while (III) is built up by chains with C.N. (La 3+ ) = 9. The experimentally determined volumes of these compounds are compared with the calculated Biltz volumes. The Raman spectra were also recorded to corroborate the presence of the planar star-shaped tricyanomethanide anion [C(CN) 3 ] – .

Single crystals of the phosphides Sm 6 Rh 30 P 19 and Lu 6 Rh 30 P 19 were synthesized from the elements with the bismuth flux technique. Polycrystalline Eu 6 Rh 30 Sb 19 was obtained from the elements by arc-melting and subsequent annealing. The structures of the phosphides were refined from single-crystal X-ray diffractometer data: P 6 3 / m , a = 1,555.07(9), c = 383.38(2) pm, wR 2 = 0.0500, 1044 F 2 values, 58 variables for Sm 6 Rh 30 P 19 and a = 1,551.99(15), c = 376.32(3) pm, wR 2 = 0.0725, 1022 F 2 values, 58 variables for Lu 6 Rh 30 P 19 . Sm 6 Rh 30 P 19 and Lu 6 Rh 30 P 19 crystallize with the Sm 6 Rh 30 Si 19 -type structure, which is closely related to the Yb 6 Co 30 P 19 type. The rhodium and phosphorus atoms build up three-dimensional [Rh 30 P 19 ] networks (225–255 pm Rh–P and 276–288 pm Rh–Rh in Sm 6 Rh 30 P 19 ) which leave hexagonal prismatic cavities for the rare earth atoms. The phosporus atoms on the c axis have distorted octahedral rhodium coordination and show disorder on the c axis (refinement with a split position). Temperature dependent magnetic susceptibility data of Eu 6 Rh 30 Sb 19 show Curie-Weiss behavior with an experimental magnetic moment of 7.78(1) µ B Eu atom −1 and θ P = −9.6(1) K, compatible with divalent europium. The europium atoms in Eu 6 Rh 30 Sb 19 are ordered antiferromagnetically at T N = 3.9(4) K which is corroborated by specific heat data. The divalent ground state of europium is manifested in the 151 Eu Mössbauer spectrum with an isomer shift value of −10.44(1) mm s −1 at 78 K. The 121 Sb Mössbauer spectrum with an isomer shift of −7.12(2) mm s −1 (envelope signal of the four crystallographically independent antimony sites) underpins the antimonide character.

Orthorhombic crystals of the composition (NH 4 ) 0.64 B 4.36 O 6.72 (OH) 0.28 (NH 3 ) 0.36 have been synthesized from boron oxide, boron nitride and boric acid in a Walker-type multianvil press under high-pressure/high-temperature conditions of 12.0 GPa and 1,300 °C. The compound crystallizes in the space group Pmn 2 1 (no. 31) with two formula units per unit cell ( Z  = 2). Its lattice parameters have been determined to be a  = 10.7906(4), b  = 4.59980(2), and c  = 4.2317(2) Å. The structure was elucidated by single-crystal X-ray diffraction, revealing a network of corner-sharing tetrahedra, which form cages containing disordered [NH 4 ] and [BNH 3 ] units. The compound was characterized using powder X-ray diffraction along with vibrational spectroscopy.

Recently, we discovered the aluminium oxonitridoborate AlB 4 O 6 N:Cr 3+ , whose high-pressure/high-temperature synthesis could be optimized in the last months. This compound shows extraordinary luminescence properties, that closely resemble the famous compound ruby, whose luminescence is characterized by two narrow R emission lines close to each other. Apart from a slight blue shift, the main difference of the luminescence of the title compound is the presence of a single R line due to nearly perfect [(Al/Cr)O 6 ] octahedra in the structure. Ruby plays a crucial role as gold standard for pressure calibration in diamond anvil cells by measuring the shift of one of these R lines with increasing pressure. However, the accuracy is limited at elevated pressure, since the two R lines broaden and eventually merge. Since the compound AlB 4 O 6 N:Cr 3+ showed only one single R line up to a pressure of at least 52 GPa, it could provide improved accuracy for the calibration of diamond anvil cells. This raises the question as to how the material behaves at even higher pressures. Therefore, we performed luminescence measurements of AlB 4 O 6 N:Cr 3+ up to 78(1) GPa in a diamond anvil cell and complemented our findings with single-crystal diffraction data (synchrotron) at elevated pressure to detect possible structural changes.

New phases in the system Hf–Ta–O–N have been synthesized and characterized by means of SEM/STEM-EDX, hot gas extraction analysis, and pXRD including Rietveld refinement. Bixbyite-type phases crystallizing in the cubic space group Ia 3 ‾ $\overline{3}$ have been prepared with three different cation ratios: Hf 0.67 Ta 1.33 N 3.11 ( a  = 9.890(2) Å), HfTaN 3 ( a  = 9.919(2) Å), and Hf 1.33 Ta 0.67 O 0.33 N 2.67 ( a  = 9.960(3) Å). In contrast to the corresponding Zr/Ta-containing phases, the lattice parameters are almost independent from the overall nitrogen/oxygen contents. This may be explained by the presence of crystallites with narrow phase widths partly covered by oxidic surface layers of variable thickness (detectable by STEM-EDX). Furthermore, a baddeleyite-type phase HfTaO 3 N (monoclinic space group P 2 1 / c , a  = 5.043(2) Å, b  = 5.101(5) Å, c  = 5.243(2) Å, β  = 99.465(9)°) has been synthesized as pale-yellow powder. No significant activity for OER was detectable.