Bouchaib Manoun

High-pressure x-ray diffraction study of Ta4AlC3

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a recently discovered phase, Ta4AlC3. This phase adopts a hexagonal structure with the space group P63∕mmc; at room conditions, the a and c parameters are 3.087(5) and 23.70(4)A, respectively. Up to a pressure of 47GPa, no phase transformations were observed. Like Ta2AlC, but unlike many related phases such as Ti4AlN3, Ti3SiC2, Ti3GeC2, and Zr2InC, the compressibility of Ta4AlC3 along the c and a axes are almost identical. The bulk modulus of Ta4AlC3, 261±2GPa, is ≈4% greater than that of Ta2AlC. Both, however, are ≈37% lower than the 345±9GPa of TaC.

Structure change of pyrochlore Sm2Ti2O7 at high pressures

Structural evolution of pyrochlore titanate Sm2Ti2O7 at high pressures was investigated by in situ Raman and x-ray diffraction methods. An intermediate phase was found at high pressures. The structure is a distorted pyrochlore, where anions are disordered after 40GPa while the cations are still somewhat ordered up to 51GPa. When the pyrochlore structure is severely distorted by external pressure, it transforms completely to an amorphous phase quenchable to room conditions.

Compression of Zr2InC to 52GPa

Using a synchrotron-radiation source and a diamond-anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Zr2InC sample. Up to a pressure of 52GPa, no phase transformations were observed. As observed in Ti3SiC2 and Ti3Si0.5Ge0.5C2, the compressibility of Zr2InC along the c axis was greater than along the a axis. The bulk modulus is 127±5GPa, with a pressure derivative of 4.25±0.3; the former is in excellent agreement with our ab initio calculations (130.9GPa). The a(3.367A) and c(15.100A) parameters from the ab initio calculations are also slightly larger than those measured here, viz., 3.35 and 14.91A. Surprisingly, a hysteresis was observed in the a-lattice parameters; they were higher upon unloading than loading. The reason for this hysteresis is not clear at this time.

High pressure study of Ti4AlN3 to 55 GPa

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti4AlN3 sample up to a pressure of 55 GPa. No phase transformations were observed. As observed in Ti3SiC2,Ti3Si0.5Ge0.5C2, and Zr2InC, the compressibility of Ti4AlN3 along the c axis was larger than along the a axis which leads to a decrease in the c∕a ratio with increasing pressure. The bulk modulus is 216±2GPa, with a pressure derivative of 3.84±0.06.Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti{sub 4}AlN{sub 3} sample up to a pressure of 55 GPa. No phase transformations were observed. As observed in Ti{sub 3}SiC{sub 2}, Ti{sub 3}Si{sub 0.5}Ge{sub 0.5}C{sub 2}, and Zr{sub 2}InC, the compressibility of Ti{sub 4}AlN{sub 3} along the c axis was larger than along the a axis which leads to a decrease in the c/a ratio with increasing pressure. The bulk modulus is 216 {+-} 2 GPa, with a pressure derivative of 3.84 {+-} 0.06.

Compression of Ti3Si0.5Ge0.5C2 to 53 GPa

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3Si0.5Ge0.5C2 sample. Up to a pressure of 53 GPa, no phase transformations were observed. As for the isostructural hexagonal Ti3SiC2, the compressibility along the c axis was greater than along a. The bulk modulus is 183±4 GPa with a pressure derivative of 3.4±0.2. This work shows that the replacement of Si by Ge in Ti3SiC2 results in a systematic decrease in the bulk moduli.

Synthesis and compressibility of Ti3(Al,Sn0.2)C2 and Ti3Al(C0.5,N0.5)2

In this paper we report on the synthesis of a composition, Ti3Al(C0.5,N0.5)2, belonging to the Mn+1AXn family of ternary layered carbides and nitrides. X-ray and selected area diffraction confirm that this compound is isostructural with Ti3SiC2; its a and c-lattice parameters are 3.0404(5) and 18.414(6) A, respectively. Chemical analysis performed by electron dispersive and electron energy loss spectroscopy confirmed the Ti3AlCN chemistry. Using a synchrotron radiation source and a diamond anvil cell, we also measured the pressure dependencies of the lattice parameters. Up to a pressure of ≈50 GPa, no phase transformations were observed. The bulk modulus is 219±4 GPa, with a pressure derivative, Ko′, of 3.7±0.3. We also fabricated the ternary Ti3AlC2, with some Sn [nominal composition Ti3(AlSn0.2)C2]. Its a and c-lattice parameters are 3.0804(7) and 18.5426(7) A, respectively. Its bulk modulus is 226±3 GPa, with a pressure derivative, Ko′, of ≈4. In both cases, the compressibility was greater along the c ...

High-pressure Raman study of the Sr2CaWO6 double perovskite

An in situ Raman spectroscopic study was conducted to explore the pressure-induced phase transformation of Sr2CaWO6 to pressures of 50.8 GPa and room temperature. Group theory yields 24 Raman active modes for Sr2CaWO6, of which 17 are observed at ambient conditions. Upon elevation of pressure to 3.2 GPa, the results suggest some structural changes, possibly a phase transition. At 10.4 GPa, new modes at high frequencies (824 and 903 cm−1) come into existence. As the material is compressed further, the intensities of the bands, especially the W–O stretching modes, observed at 824 and 903 cm−1 become stronger, while those centred at 863 and 937 cm−1 (at 10.4 GPa) decrease significantly, until disappearance. These changes in the spectrum indicate clearly that Sr2CaWO6 undergoes a phase transition at 9.7 ± 0.7 GPa. Upon release of pressure to ambient conditions, a new phase is observed with ten bands compared to the 17 observed in the original phase.

A high-pressure Raman spectroscopic study of hafnon, HfSiO4

Abstract Raman spectra of synthetic HfSiO4 were determined to pressures of 38.2 GPa. Changes in the spectra indicate that HfSiO4 undergoes a room-temperature phase transition from the hafnon structure (I41/amd space group) to the scheelite structure (I41/a space group) at a pressure of ~19.6 GPa. Upon release of pressure to ambient conditions, the spectra indicate that the sample retains the scheelite structure. Zircon has been classified previously as the least compressible tetrahedrally coordinated silicate known. However, pressure derivatives of the peak positions in hafnon are smaller than those in zircon, and suggest that hafnon is more incompressible than zircon. Furthermore, the pressure derivatives also suggest that the high-pressure, scheelite-structured HfSiO4 phase is more incompressible than the scheelite-structured ZrSiO4 (reidite). Thus, the post-hafnon phase appears to be even more incompressible than hafnon, which would make it the least compressible tetrahedrally coordinated silicate known to date.

Phase transitions in heated Sr2MgTeO6 double perovskite oxide probed by X-ray diffraction and Raman spectroscopy

Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.

Catalytic effect of potassium in Na1−xKxCdPb3(PO4)3 to detect mercury (II) in fish and seawater using a carbon paste electrode

In this paper, we report a synthesis of a new lacunar apatite, KCdPb3(PO4)3, using solid state method, and its application as modifier of carbon paste electrode (KLA-CPE) to determine mercury (II). Sodium replacement with potassium induced a linear variation of the crystallographic parameters a and c according to Vegards law and led to amplify the electrical signal of the working electrode. The peak currents of mercury (II) increased linearly with their concentration at the range from 2.0×10(-7)molL(-1) to 1.0×10(-4)molL(-1) using differential pulse anodic stripping voltammetry. The detection limit was found to be 1.11×10(-8)molL(-1). The use of this electrochemical sensor has been successfully implemented for the determination of Hg (II) in seawater and fish samples. The obtained results were found to be very satisfactory.