Primitive Tetragonal Structure Research Articles

High-pressure synthesis of novel hydrides in Mg–RE–H systems (RE = Y, La, Ce, Pr, Sm, Gd, Tb, Dy)

The high-pressure synthesis of new hydrides of Mg–RE–H systems, where RE = Y, La, Ce, Pr, Sm, Gd, Tb and Dy, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In Mg–Y–H system, newly found MgY 2H y with a FCC-type structure has been prepared. In MgH 2– x mol% REH (REH = LaH 3, CeH 2.5 and PrH 3), new hydrides with primitive tetragonal structure were synthesized around x = 25–33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c = 0.4970 nm at x = 25 in Mg–La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1, 3.7 and 3.9 mass% in Mg–La, Ce and Pr systems, respectively, and the chemical formulae were found to correspond to Mg 3LaH 9, Mg 3CeH 8.1 and Mg 3PrH 9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg 3LaH 9: 614 K, Mg 3CeH 8.1: 609 K, Mg 3PrH 9: 630 K) with an endothermic reaction. In MgH 2– x mol% hREH (hREH = GdH 3, TbH 3 and DyH 3), new hydrides with FCC-type structure were synthesized around x = 67.

Synthesis and Crystal Structure of New Hydrides in Mg-RE Systems under High-Pressure (RE = La, Ce, Pr)

The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = La, Ce and Pr, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In MgH2-xmol%REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25 - 33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c= 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1 mass%, 3.7 mass% and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulas were found to correspond to Mg3LaH9, Mg3CeH8.1 and Mg3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction.

A new Ti/H phase transformation in the H2+titanium alloy studied by x-ray diffraction, nuclear reaction analysis, elastic recoildetection analysis and scanning electron microscopy

The titanium hydrogenation process in the H2+ implantedTi225 titanium alloy has been studied in this work. The Ti/H phase transformationfrom hydrogen solid solution (hcp) to gamma phase titanium hydride (TiH(γ))with a primitive tetragonal structure and then to a titanium dihydride(TiH2(x))with a body centred tetragonal structure has been characterized byx-ray diffraction, nuclear reaction analysis and elastic recoil detectionanalysis. This process is very different from the usual hydrogenationmechanism, in which the delta phase titanium dihydride (TiH2(δ))with a face centred cubic structure is always involved. Both of the TiH(γ) andTiH2(x)are rare phases, which are formed under extreme conditions. The TiH(γ) wasconsidered to be a metastable phase in low hydrogen concentration titanium, and theTiH2(x)phase has not yet been notated in the present Ti/H phase list. The characteristics of theTiH2(x)are unclear, but it is very stable at room temperature and exists as a mixturestate with the titanium. A saturated fraction of the hydride to titaniumphase has been obtained as about 15% (H/Ti ∼ 0.3) in a H2+implanted sample.

Pressure-induced phase changes of argon hydrate and methane hydrate at room temperature

High-pressure experiments of argon hydrate and methane hydrate were performed using a diamond anvil cell in a pressure range of 0.2 to 10.0GPa at room temperature. In-situ X-ray diffractometry and optical microscopy revealed that two high pressure structures of argon hydrate, a primitive tetragonal structure and a body-centered orthorhombic structure, existed under pressures of up to 6.5GPa. The structural analysis showed that the tetragonal structure was composed solely of 14-hedra accommodating two argon atoms, and that the body-centered orthorhombic structure belonged to a“filled-ice”structure, i.e., a new type of structure in a water-guest system. As for methane hydrate, three high-pressure structures, a hexagonal structure, a primitive orthorhombic structure, and a body-centered orthorhombic structure, were found. The structural analysis indicated that the hexagonal structure was a modified structure of a hexagonal one reported at ambient pressure, and that the latter orthorhombic structure was the“filled-ice”structure.

Phase equilibria in the system Fe-Ni-S at 500.DEG.C. and 400.DEG.C..

Phase equilibria in the system Fe-Ni-S were investigated by dry synthesis at 500°C and 400°C using three elements (Fe, Ni and S) and two synthetic sulfides (FeS and NiS). Phase diagrams of this ternary system at these two temperatures were obtained. The extent of the monosulfide solid solution (mss) is complete at 500°C and 400°C. The d(102)-values of the mss are increasing with the increasing Fe/(Fe+Ni) ratio and are decreasing with the increasing sulfur content of the mss. Pentlandite has the solid solution areas ranging from (Fe0.66Ni0.34)9.02S8.00 to (Fe0.30Ni0.70)9.35S8.00 at 500°C and from (Fe0.70Ni0.30)9.39S8.00 to (Fe0.41Ni0.59)9.24S8.00 at 400°C. Violarite has the solid solution area ranging from (Fe0.16Ni0.84)3.02S4.00 to (Fe0.34Ni0.66)3.00S4.00 at 400°C and does not exist at 500°C. Godlevskite is stable at 400°C and it transforms to α-Ni7S6 phase at 500°C run. Tie lines of pentlandite to godlevskite at 400°C and pentlandite to α-Ni7S6 phase at 500°C are stable. On the Fe-Ni join, two kinds of Fe-Ni alloys (α-iron and γ-phase) and pure nickel are stable. Alfa-iron has a body-centered cubic structure and pure nickel has a face-centered cubic structure. Gamma-phase has a primitive tetragonal structure and the FeNi3 phase is included in the γ-phase solid solution.

Ternary Intermetallic Compounds LnMn2Al10 (Ln = Y, La-Nd, Sm, Gd-Dy) and LnRe2Al10 (Ln = Ce, Pr, Sm) with CaCr2Al10-Type Structure

Abstract The twelve title compounds have been prepared for the first time. Their CaCr2Al10-type structure (P4/nmm, Z = 4) was refined from single-crystal X-ray data for the three representatives TbMnAl10 (a = 1274.3(2) pm, c = 511.4(2) pm, R = 0.025 for 680 structure factors F and 43 variable parameters V), CeRe2Al10 (a = 1295.5(5) pm, c = 517.2(4) pm, R = 0.054 for 810 F and 46 V), and SmRe2Al10 (a = 1291.5(2) pm, c = 516.5(1) pm, R = 0.021 for 622 F and 46 V). The atomic positions of the lanthanoid and transition metal atoms are fully occupied. Significant deviations from the full occupancies were observed for two aluminum sites in TbMn2Al10 and for all five aluminum sites of the two rhenium-containing compounds, resulting in the compositions TbMn2Al9.63(2), CeRe2Al9.52(8), and SmRe2Al9.16(9). The cell volume of CeRe2Al10 and to a smaller extent also that of CeMn2Al10 indicate mixed or intermediate +III/+IV valencies of the cerium atoms in these compounds. The structural relationships between the three closely related body-centered tetragonal structures of ThMn12, CeMniAl8, DyFe6Al6 and the primitive tetragonal structure of CaCr2Al10 are briefly discussed.

Microstructure Development in Laser-Processed Al–Ti–Ni Alloys with 25 At. % Ti

The microstructure of laser-processed (Al1−xNix)3 Ti with Ni content ranging from 5 to 15 at. % has been studied by scanning-and transmission-electron microscopy (SEM and TEM). All samples contain Al-rich dendrites with Ni-rich interdendritic phases. The dendrites in the 5 at. % Ni alloy consist of the Al3Ti phase with the DO22 type structure, whereas the alloys containing 8 to 15 at. % Ni consist of the Al67Ni8Ti25 phase with the L12-type structure. The lattice parameter of the L12 type structure of Al67Ni8Ti25 was determined by comparing the Higher Order Laue Zone (HOLZ) line patterns in experimental and calculated convergent beam electron diffraction disks. The lattice parameter was found to be a = 0.3935 ± 0.0003 nm. Within the L12 type regions of the alloy with 8 at. % Ni, precipitates with a new primitive tetragonal structure was found. The cell dimensions are a = 0.39 nm and c = 1.18 nm. AlNTi2 with Ti: Al ratio equal to 2.0 ± 0.2 was found as needles in interdendritic regions. The cell dimensions are consistent with a = 0.299 nm and c = 1.361 nm and space group P63/mmc.

Growth of Single Crystals in the Systems withR–Rh–B andR–Rh–B–C (R=Rare Earth Element) from Molten Copper Flux

A slow cooling method using molten copper as a flux was applied for crystal growth in the systemsR–Rh–B andR–Rh–B–C (R=rare earth element).Ternary borides: Single crystals ofRRh3B2(R=Gd, Dy, Er, Tm, Yb, and Lu),RRh4B4(R=Sm, Dy, Er, and Tm), andRRh3B (R=Sm, Gd, Er, and Tm) were successfully obtained. Crystals of ErRh3B2are hexagonal rectangulars belonging to the monoclinic systema=0.5355(1) nm,b=0.9282(1) nm,c=0.3102(1) nm, andβ=90.89(3)°. A super lattice appears along both theaand thecaxes with the periods of 3aand 6c, respectively. Single crystals of ErRh4B4were obtained as rectangulars with a primitive tetragonal structure:a=0.5292(4) nm andc=0.7379(3) nm. Single crystals of ErRh3B were extracted as cubes. ErRh3B is cubic witha=0.41466(1) nm. PrRh4.8B2crystallized as hexagonal plates. This new compound is orthorhombic:a=0.9697(4) nm,b=0.5577(2) nm, andc=2.564(3) nm.Quaternary borocarbides: Single crystals of the new tetragonal compounds ofRRh2B2C have been obtained forR=Er and Gd as thin plates. Lattice parameters of e.g., ErRh2B2C, area=0.36848(2) nm andc=1.05520(3) nm.

Magnetic behavior in a series of cerium ternary intermetallics: Ce2T2In (T=Ni, Cu, Rh, Pd, Pt, and Au).

A group of ternary cerium compounds ${\mathrm{Ce}}_{2}$${\mathit{T}}_{2}$In (T=Ni, Cu, Rh, Pd, Pt, and Au) has been synthesized. As found from single-crystal and powder x-ray-diffraction studies, all these phases crystallize in a primitive tetragonal structure of the ${\mathrm{Mo}}_{2}$${\mathrm{FeB}}_{2}$ type. Magnetic measurements (magnetization, dc and ac susceptibility) have revealed the physical properties of these intermetallics to be mainly governed by the 4f-d hybridization. Depending on the filling of the transition metal d band the ground state in ${\mathrm{Ce}}_{2}$${\mathit{T}}_{2}$In changes from a nonmagnetic to a well localized magnetic regime. It was proved that ${\mathrm{Ce}}_{2}$${\mathrm{Ni}}_{2}$In and ${\mathrm{Ce}}_{2}$${\mathrm{Rh}}_{2}$In are intermediate-valence systems, ${\mathrm{Ce}}_{2}$${\mathrm{Pt}}_{2}$In is a strongly temperature-dependent paramagnet, whereas ${\mathrm{Ce}}_{2}$${\mathrm{Cu}}_{2}$In, ${\mathrm{Ce}}_{2}$${\mathrm{Pd}}_{2}$In, and ${\mathrm{Ce}}_{2}$${\mathrm{Au}}_{2}$In order magnetically at low temperatures. Measurements of the electrical resistivity have corroborated the intermediate-valence behavior in ${\mathrm{Ce}}_{2}$${\mathrm{Ni}}_{2}$In and ${\mathrm{Ce}}_{2}$${\mathrm{Rh}}_{2}$In. In turn, the resistivity of the remaining ternaries studied was found to be determined by an interplay of Kondo scattering and crystal-field effects. For ${\mathrm{Ce}}_{2}$${\mathrm{Pt}}_{2}$In which behaves like a spin-fluctuating system due to strong Kondo-type interactions a nonmagnetic heavy-fermion ground state probably occurs. \textcopyright{} 1996 The American Physical Society.

Raman Scattering and X-Ray Diffraction Study of a Phase Transition in (ND4)2TeBr6

Raman spectra of (ND4)2TeBr6 were recorded in the temperature range 5–300 K. A continuous minimum of the Raman shift and a continuous maximum of the linewidth of theA1gmode of the TeBr62− octahedron were observed atTc=68 K. Also, theT2gmode of the TeBr62− octahedron continuously split into two lines belowTc. X-ray diffraction measurements at 10 K indicate that the low-temperature phase has a primitive tetragonal structure, and an antiferro-rotation of the TeBr62− octahedra is associated with the transition. This behaviour indicates a displacive phase transition atTc.

Magnetic and resistivity studies of GdNi2Sn2, GdCu2Sb2 and GdNi2Sb2 compounds

Ternary GdNi2Sn2, GdCu2Sb2 and GdNi2Sb2 compounds crystallize in the primitive tetragonal CaBe2Ge2-type structure. The compounds investigated are antiferromagnetic below 7 K, 11 K and 6 K respectively. Large negative paramagnetic Curie temperatures accompany these low Néel temperatures. This may be related to the frustration of magnetic interactions. At temperatures lower than TN anomalies in magnetization vs. magnetic field curves and resistivity can be attributed either to a change in magnetic structure or to spin-flopping phenomena.

The electrical resistivity of the new UCu 2Sn 2 compound

A new uranium ternary compound UCu 2Sn 2 has been obtained, crystallizing with the primitive tetragonal structure of CaBe 2Ge 2-type (space group P4/nmm). The electrical resistivity versus temperature ( ϱ( T)) depends on the annealing procedures. The ϱ( T) curve for the annealed sample exhibits anomalous behaviour with a gradual increase towards lower temperatures followed by a broad maximum below 110 K and steep decrease below approximately 20 K which may indicate Kondo-like behaviour.

Oxides of the type TlSr 2Cu 1− xMxO 5 ( M = Fe, Co) having the 121 structure

Oxides of the type TlSr 2Cu 1− x M x O 5 ( M = Fe, 0.5 ≤ x ≤ 0.75; M = Co, 0.3 ≤ x ≤ 0.5) have been synthesized and characterized for the first time. These oxides were monophasic and crystallized in a primitive tetragonal structure ( c-parameters ∼9.0 Å. Lattice parameters vary systematically with x. All the oxides show semiconducting behavior. Neutron powder diffraction study on TlSr 2Cu 0.4Fe 0.6O 5−δ shows structural features similar to those of other 121 oxides, but has comparatively less disorder in the TlO plane and has axially compressed Cu FeO 6 octahedra.

Synthesis microstructure and superconducting properties of Ce-Doped Ti-Sr-Ca-Cu-O

A new Tl 1− x Ce x Sr 2CaCu 2O 7 compound with x=0.25, which forms a primitive tetragonal structure with a=b=3.816 A ̊ and c=12.112 A ̊ , has been synthesized in nearly pure form. The structure has been confirmed for the heavy atoms at the microstructural level by high resolution lattice imaging techniques. Selected area electron diffraction did not indicate the presence of structural modulations. The presence of Ce has been confirmed by analytical electron microscopic methods and by X-ray photoemission spectroscopy; the latter also indicates that cerium is present as Ce +4 ions. SQUID magnetometry, AC susceptibility and four-probe resistance measurements indicate superconductivity with a T c between 62 and 68 K. Meissner fractions greater than 10% of ideal diamagnetism signal the presence of bulk superconductivity in the samples. The nature of the substitution process, and the reasons for a 20 K drop in T c from a value of near 85 K for the isostructural Tl 0.5Pb 0.5Sr 2CaCu 2O 7 superconductor, are discussed.

Polymorphism and physical properties of LnNi2As2 compounds (Ln = La → Gd)

Ternary BaAl4-type derivative structures are frequently found with lanthanoïd transition metal silicides, germanides and pnictides with the Ln atoms occupying the Ba sites and the other atoms distributed in an ordered fashion on the Al sites. The ternary phase diagrams LnNiAs were investigated and the compounds LnNi2As2 were obtained with Ln = La → Gd. They crystallize either with the body-centered tetragonal ThCr2Si2-type (L.T. form), space group I4/mmm, or primitive tetragonal CaBe2Ge2-type structure (H.T. form), space group P4/nmm. The X-ray structures of LaNi2As2 and CeNi2As2 were refined down to residual values of 0.059 and 0.053 in their L.T. and of 0.028 and 0.060 in their H.T. forms. Electrical and magnetic measurements were performed on single crystals; they exhibit a metallic conductivity and a magnetic ordering at low temperature when Ln = Ce, Pr, Sm, Eu. Above 50 K, the compounds have a normal C.W. behavior with magnetic moments consistent with those of the free Ln3+ ions, except for Eu which is divalent. LaNi2As2 (L.T. and H.T.) is paramagnetic slightly temperature dependent.

Antiferromagnetic Ordering in the Ternary Rare Earth Cobalt Borides RCo4B4 (R=Ce, Gd, Tb, Dy, Ho, Er, Tm, Lu)

Antiferromagnetic Néel temperatures (TN) are reported for magnetic rare earth cobalt compounds RCo4B4 (R=Gd, Tb, Dy, Ho, Er, Tm) which crystallize with the primitive tetragonal CeCo4B4-type structure. The maximum TN of 3.68 K was observed in TbCo4B4, while TmCo4B4 has the lowest ordering temperature of 0.17 K. No magnetic transition was observed for CeCo4B4 and LuCo4B4 down to 60 mK. The complex evolution from antiferromagnetic order in HoCo4B4 (TN=1.91 K) to ferromagentic order in HoRh4B4 (TC=6.56 K) of the pseudoternary system Ho(Rh1-xCox)4B4 is briefly discussed.

Magnetic behaviour of ternary silicides CeT 2Si 2 (T ≡ Ru, Rh, Pd, Os, Ir, Pt) and boron substitution in Ce{Ru, Os} 2Si 2− xB x

The ternary silicides CeT 2Si 2 have been investigated with respect to crystal chemistry and magnetochemical behaviour. Ce{Ru, Rh, Pd, Os} 2Si 2 crystallize with the body-centred tetragonal ThCr 2Si 2-type structure, whereas CePt 2Si 2 and h-CeIr 2Si 2 adopt the primitive tetragonal CePt 2Si 2-type structure and CaBe 2Ge 2-type structure respectively. h-CeIr 2Si 2 exhibits a phase transition into a ThCr 2Si 2-type low temperature modification ( T u ≈ 920 ° C). The magnetic behaviour at low temperatures is characterized by the onset of antiferromagnetic ordering in the case of CeRh 2Si 2 whereas a non-magnetic cerium ground state is proposed for the remaining platinum metal members Ce{Ru, Pd, Os, Ir, Pt} 2Si 2, which was interpreted in terms of the interconfiguration fluctuations model. Boron solubility in Ce{Ru, Os} 2Si 2− x B x at 1000 °C was found to be limited at x ≈ 1 and resulted in a rather small change in the susceptibility values as compared with those of the ternary silicides CeRu 2Si 2 and CeOs 2Si 2.

The HoGa system in the 66.7–100 at.% Ga range

The HoGa system was re-examined on the gallium-rich side by differential thermal analysis, X-ray diffraction, metallography and scanning electron microscopy with energy-dispersive analysis. The existence of HoGa 6 was established. It has a primitive tetragonal structure, PuGa 6 type, with the following lattice parameters: a = 5. 918 A ̊ ; c = 7.543 A ̊ . Unlike the systems of cerium, neodymium and gadolinium with gallium, no solid solubility of gallium in HoGa 2 was found. The lack of solid solubility is explained in terms of relative distortion of the unit cell of HoGa 2 on replacing a holmium atom by gallium atoms. The lattice parameters of HoGa 2 and HoGa 3 were confirmed.

The gallium-rich side of the Nd-Ga and Ce-Ga systems

The existence of an intermetallic compound of the type RGa 6 (R  rare earth) on the gallium-rich side of the Nd-Ga and Ce-Ga systems was established. The compounds NdGa 6 and CeGa 6 have a primitive tetragonal structure with the following lattice parameters: NdGa 6 a = 5.996 ± 0.001 A ̊ b = 7.620 ± 0.001 A ̊ CeGa 6 a = 6.03 A ̊ b = 7.632 A ̊ A large solid solubility range exists between the RGa 2-type compound and Nd-80at.%Ga or Ce-78at.%Ga. This phase has a hexagonal structure, the lattice parameters of which increase with the concentration of gallium.

Superconductivity, magnetism and metastability of new ternary iridium borides

Superconductivity has been found in the rare earth iridium borides with the general formula MIr 4B 4 and in the pseudoternary (Y xLu 1−x)−Ir 4B 4 system, M being a rare earth element. The pure phase in itself is only metastable at best. The compounds were found to crystallize with the primitive tetragonal CeCo 4B 4-type structure. The close correlation between superconductivity, magnetism and structural metastability is demonstrated with the study of the pseudoternary systems M(Ir xRh 1−x) 4B 4 ( x = 0.1 and 0.5) and Er(Ir xRh 1−x) 4B 4.