Isosymmetrical phase transition in α-YbV4O8

2008 ◽  
Vol 64 (6) ◽  
pp. 652-660 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andy N. Fitch ◽  
Wolfgang Morgenroth ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
Three Dimensional ◽  
Structure Type ◽  
Charge Ordering ◽  
Gap Formation ◽  
Magnetic Susceptibility Data ◽  
First Order ◽  
Susceptibility Data ◽  
Transition Mechanism ◽  
Α Phase

The structure of YbV4O8 is related to the CaFe2O4 structure type. VO6 octahedra form a three-dimensional framework with tunnels in which the Yb3+ ions are incorporated. Two different polymorphs α and β are known and differ mainly in the arrangement of the Yb ions within the framework. We studied the structure and magnetic properties of α-YbV4O8 as a function of temperature. At approximately 70 K α-YbV4O8 undergoes a first-order isosymmetrical phase transition (P21/n → P21/n). While in the high-temperature α phase the three V3+ and one V4+ are disordered over the four symmetrically independent octahedral sites, in the low-temperature α′ phase complete charge ordering is observed. The transition is accompanied by a paramagnetic–paramagnetic anomaly in the magnetic susceptibility data which can be interpreted on the basis of spin-gap formation. The transition mechanism in the α polymorph is very similar to that observed earlier in the β polymorph at 185 K.

SrCo2Sn8 and BaCo2Sn8: Tin-rich Stannides with Distorted SnSn6 Octahedra within Three-dimensional [Co2Sn8] Networks

2013 ◽  
Vol 68 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Christian Schwickert ◽  
Rainer Pöttgen
Keyword(s):  
Three Dimensional ◽  
Structure Type ◽  
Temperature Dependent ◽  
Magnetic Susceptibility Data ◽  
Susceptibility Data ◽  
Dimensional Network ◽  
Covalently Bonded ◽  
Distorted Octahedral ◽  
Pauli Paramagnetism ◽  
Tin Coordination

The tin-rich stannides SrCo2Sn8 and BaCo2Sn8 were synthesized from the elements in sealed tantalum tubes. They crystallize with a new structure type, space group Cccm with a=1006.0(3), b=1514.4(6), c=1385.0(6) pm for SrCo2Sn8 and a=1032.8(2), b=1516.8(3), c=1405.1(3) pm for BaCo2Sn8. The structure of the barium compound was refined on the basis of single-crystal Xray diffractometer data: wR2=0.0450, 1715 F2 values, 57 variables. The cobalt atoms have seven nearest tin neighbors with Co-Sn distances ranging from 257 to 273 pm. These CoSn7 units are condensed via common rectangular faces to [Co2Sn10] double units which build up a covalently bonded three-dimensional network through Sn-Co-Sn bridges. Larger voids left by this network are filled by the barium and the Sn2 atoms. The latter have distorted octahedral tin coordination with Sn2- Sn distances of 311 - 315 pm. The barium atoms have 13 nearest tin neighbors (352 - 399 pm Ba-Sn). Temperature-dependent magnetic susceptibility data of BaCo2Sn8 show Pauli paramagnetism.

Intermediate-valent Cerium in CeRu2Mg5

2010 ◽  
Vol 65 (10) ◽  
pp. 1185-1190 ◽  
Author(s):  
Stefan Linsinger ◽  
Matthias Eul ◽  
Ute Ch. Rodewald ◽  
Rainer Pöttgen
Keyword(s):  
High Frequency ◽  
Three Dimensional ◽  
Magnetic Ordering ◽  
Structure Type ◽  
Formula Unit ◽  
Temperature Dependent ◽  
Magnetic Susceptibility Data ◽  
Susceptibility Data ◽  
Intermediate Valent ◽  
Cerium Atom

The magnesium-rich compound CeRu2Mg5 was synthesized by high-frequency melting of the elements in a sealed tantalum ampoule. CeRu2Mg5 crystallizes with a new tetragonal structure type: P42/ncm, a = 961.1(1), c = 723.2(1) pm, wR2 = 0.0284, 481 F2 values and 25 variables. The striking structural motifs in CeRu2Mg5 are short Ce-Ru distances of 232 pm. Each cerium atom is connected to two ruthenium atoms within a three-dimensional [Ru2Mg5] network. CeRu2Mg5 has a pronounced magnesium substructure with short Mg-Mg distances in the range 302 - 341 pm. The short Ce-Ru distances are a consequence of the almost tetravalent character of the cerium atoms. Temperature-dependent magnetic susceptibility data show intermediate-valent behavior of the cerium atoms (0.9(1) μB per formula unit) and no magnetic ordering down to 3 K.

The equiatomic intermetallics REPtCd (RE= La, Ce, Pr, Nd, Eu) and magnetic properties of CeAuCd

2015 ◽  
Vol 70 (3) ◽  
pp. 197-202 ◽  
Author(s):  
Michael Johnscher ◽  
Frank Tappe ◽  
Oliver Niehaus ◽  
Rainer Pöttgen
Keyword(s):  
Phase Transition ◽  
Three Dimensional ◽  
Induction Melting ◽  
Antiferromagnetic Phase ◽  
Crystal Data ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
Magnetic Susceptibility Data ◽  
X Ray ◽  
Susceptibility Data

AbstractThe cadmium intermetallics REPtCd (RE = La, Ce, Pr, Nd, Eu) and CeAuCd were synthesized by induction-melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. The samples were characterized by powder X-ray diffraction. The structures of CePtCd (ZrNiAl type, $P\bar 62m,$a = 763.8(6), c = 409.1(4) pm, wR2 = 0.0195, 298 F2 values, 14 variables) and EuPtCd (TiNiSi type, Pnma, a = 741.3(2), b = 436.4(1), c = 858.0(4) pm, wR2 = 0.0385, 440 F2 values, 20 variables) were refined from single-crystal data. The REPtCd structures exhibit three-dimensional networks of corner- and edge-sharing Cd@Pt2/6Pt2/3 and Cd@Pt4/4 tetrahedra, which leave cages for the rare earth atoms. Temperature-dependent magnetic susceptibility data of CeAuCd reveal a paramagnetic to antiferromagnetic phase transition at TN = 3.7(5) K.

scholarly journals Monoclinic–orthorhombic first-order phase transition in K2ZnSi5O12 leucite analogue; transition mechanism and spontaneous strain analysis.

2021 ◽  
pp. 1-20
Author(s):  
Anthony M.T. Bell ◽  
Francis Clegg ◽  
Christopher M.B. Henderson
Keyword(s):  
Phase Transition ◽  
Strain Analysis ◽  
Phase Region ◽  
Martensitic Transition ◽  
Two Phase ◽  
Spontaneous Strain ◽  
First Order ◽  
Transition Mechanism ◽  
First Order Phase Transition ◽  
Increasing Temperature

Abstract Hydrothermally synthesised K2ZnSi5O12 has a polymerised framework structure with the same topology as leucite (KAlSi2O6, tetragonal I41/a), which has two tetrahedrally coordinated Al3+ cations replaced by Zn2+ and Si4+. At 293 K it has a cation-ordered framework P21/c monoclinic structure with lattice parameters a = 13.1773(2) Å, b = 13.6106(2) Å, c = 13.0248(2) Å and β = 91.6981(9)°. This structure is isostructural with K2MgSi5O12, the first cation-ordered leucite analogue characterised. With increasing temperature, the P21/c structure transforms reversibly to cation-ordered framework orthorhombic Pbca. This transition takes place over the temperature range 848−863 K where both phases coexist; there is an ~1.2% increase in unit cell volume between 843 K (P21/c) and 868 K (Pbca), characteristic of a first-order, displacive, ferroelastic phase transition. Spontaneous strain analysis defines the symmetry- and non-symmetry related changes and shows that the mechanism is weakly first order; the two-phase region is consistent with the mechanism being a strain-related martensitic transition.

Ferromagnetic interactions in a dicyanamide-bridged multinuclear metal-organic framework [Pr3NH]+ [Mn(dca)3]−·H2O

2019 ◽  
Vol 74 (6) ◽  
pp. 485-489
Author(s):  
Yuan Huang ◽  
Xiu-feng Yu ◽  
Zhen Rong ◽  
Yi-chun Ai ◽  
Kun Qian ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Measurements ◽  
Metal Organic Framework ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Magnetic Susceptibility Data ◽  
X Ray ◽  
Susceptibility Data ◽  
Metal Organic ◽  
Ferromagnetic Interactions

AbstractA new complex [Pr3NH]+ [Mn(dca)3]− · H2O (dicyanamide = dca−) was synthesized, in which the Mn2+ cations are bridged by end-to-end dca anions to form three-dimensional [Mn(dca)3]nn− networks and tripropylammonium cations reside in the cavities of these networks. The complex has been characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, and magnetic measurements. Magnetic susceptibility data indicate ferromagnetic interactions among the MnII ions.

Structure and Magnetism of REPtMg (RE = Pr,Nd, Sm)

2002 ◽  
Vol 57 (5) ◽  
pp. 488-494 ◽  
Author(s):  
Rainer Kraft ◽  
Gunter Kotzyba ◽  
Rolf-Dieter Hoffmann ◽  
Rainer Pöttgen
Keyword(s):  
Spin Structure ◽  
Three Dimensional ◽  
Point Of View ◽  
Single Crystal Diffraction ◽  
Magnetic Susceptibility Data ◽  
X Ray ◽  
Susceptibility Data ◽  
Complex Spin ◽  
Ferromagnetic Ordering ◽  
Ordered State

New magnesium based intermetallic compounds PrPtMg, NdPtMg and SmPtMg were synthesized from the elements by reaction in sealed tantalum tubes in a high-frequency furnace. The three compounds were investigated by X-ray powder and single crystal diffraction: ZrNiAl type, space group P6̄2m, a = 752.34(8), c = 412.66(4) pm, wR2 = 0.0668, 341 F2 values, 14 variables for PrPtMg, a = 748.80(8), c = 411.52(4) pm, wR2 = 0.0521, 196 F2 values, 14 variables for NdPtMg and a = 743.90(5), c = 409.80(3) pm, wR2 = 0.0489, 248 F2 values, 12 variables for SmPtMg. From a geometrical point of view these structures are composed of two types of platinum centered trigonal prisms, i. e. [Pt1Mg3RE6] and [Pt2Mg6RE3]. These prisms are condensed via common edges and faces. Together the platinum and magnesium atoms build three-dimensional [PtMg] networks in which the rare earth atoms are located in distorted pentagonal channels. Magnetic susceptibility data of PrPtMg show Curie-Weiss behaviour with an experimentalmagnetic moment of 3.59(2) μB and a paramagnetic Curie temperature of 7.5(5) K. Ferromagnetic ordering is detected at TC = 8.0(5) K with a magnetic moment of 1.75(5) μB/Pr at 4.5 K and 5 T. SmPtMg orders ferromagnetically below 52(1) K with a presumably complex spin structure in the ordered state.

scholarly journals THREE-DIMENSIONAL GONIHEDRIC SPIN SYSTEM

2002 ◽  
Vol 17 (12) ◽  
pp. 751-761 ◽  
Author(s):  
G. KOUTSOUMBAS ◽  
G. K. SAVVIDY
Keyword(s):  
Phase Transition ◽  
Spin System ◽  
Order Approximation ◽  
Three Dimensional ◽  
Extrinsic Curvature ◽  
Original Model ◽  
Coupling Constants ◽  
Spin Interaction ◽  
First Order ◽  
Isotropic Point

We perform Monte–Carlo simulations of a three-dimensional spin system with a Hamiltonian which contains only four-spin interaction term. This system describes random surfaces with extrinsic curvature – gonihedric action. We study the anisotropic model when the coupling constants βS for the space-like plaquettes and βT for the transverse-like plaquettes are different. In the two limits βS = 0 and βT = 0 the system has been solved exactly and the main interest is to see what happens when we move away from these points towards the isotropic point, where we recover the original model. We find that the phase transition is of first order for βT = βS ≈ 0.25, while away from this point it becomes weaker and eventually turns to a crossover. The conclusion which can be drawn from this result is that the exact solution at the point βS = 0 in terms of 2D-Ising model should be considered as a good zero-order approximation in the description of the system also at the isotropic point βS = βT and clearly confirms the earlier findings that at the isotropic point the original model shows a first-order phase transition.

HIGH-DENSITY EXPANSION FOR THE SPINLESS FERMION MODEL I: FIRST ORDER IN 1/z AND HORWITZ-CALLEN RENORMALIZATION

1988 ◽  
Vol 02 (03n04) ◽  
pp. 483-520 ◽  
Author(s):  
M. BARTKOWIAK ◽  
P. MÜNGER ◽  
R. MICNAS
Keyword(s):  
Three Dimensional ◽  
Charge Ordering ◽  
High Density ◽  
Fermion Model ◽  
First Order ◽  
Diagrammatic Technique ◽  
Spinless Fermion ◽  
Density Expansion ◽  
Band Case ◽  
Second Order Phase Transition

A diagrammatic technique for Hubbard's operators is employed to perform systematically the high-density expansion for the three-dimensional spinless fermion model. The molecular field theory is obtained by the zero-order renormalization of blocks. Summation of the first order diagrams is carried out in both selfconsistent and correctional way. It turns out that the charge ordering parameter, calculated self-consistently, has a jump for a certain medial temperature. We have also shown, that the Horwitz-Callen renormalization leads to the first or second order phase transition, depending on t/W and fails when this ratio is large enough. The phase diagrams of the system for the half-filled band case, derived in both unrenormalized and renormalized first order of high-density expansion are presented.

Ternary Indides REMgIn (RE = Y, La–Nd, Sm, Gd–Tm, Lu). Synthesis, Structure and Magnetic Properties

2004 ◽  
Vol 59 (5) ◽  
pp. 513-518 ◽  
Author(s):  
Rainer Kraft ◽  
Martin Valldor ◽  
Daniel Kurowski ◽  
Rolf-Dieter Hoffmann ◽  
Rainer Pöttgen
Keyword(s):  
Magnetic Moments ◽  
Three Dimensional ◽  
Temperature Dependent ◽  
Variable Parameters ◽  
Magnetic Susceptibility Data ◽  
X Ray ◽  
Susceptibility Data ◽  
Sample Chamber ◽  
Trigonal Prismatic Coordination ◽  
Trigonal Prismatic

Abstract The equiatomic rare earth-magnesium-indium compounds REMgIn (RE = Y, La-Nd, Sm, Gd- Tm, Lu) were prepared from the elements in sealed tantalum tubes inside a water-cooled sample chamber of an induction furnace. All compounds were characterized through their X-ray powder patterns. They crystallize with the hexagonal ZrNiAl type structure, space group P6̄̄2m, with three formula units per cell. The structure of SmMgIn was refined from X-ray single crystal diffractometer data: a = 761.3(2), c = 470.3(1) pm, wR2 = 0.0429, 380 F2 values and 14 variable parameters. The DyMgIn, HoMgIn, and TmMgIn structures have been analyzed using the Rietveld technique. The REMgIn structures contain two cystallographically independent indium sites, both with tri-capped trigonal prismatic coordination: In1Sm6Mg3 and In2Mg6Sm3. Together the magnesium and indium atoms form a three-dimensional [MgIn] network with Mg-Mg distances of 320 and Mg-In distances in the range 294 - 299 pm. Temperature dependent magnetic susceptibility data show Curie-Weiss behavior for DyMgIn, HoMgIn, and TmMgIn with experimental magnetic moments of 11.0(1) μB/Dy atom, 10.9(1) μB/Ho atom, and 7.5(1) μB/Tm atom. The three compounds order antiferromagnetically at TN = 22(2) K (DyMgIn), 12(1) K (HoMgIn), and 3(1) K (TmMgIn).

Intermediate-valent Cerium in Ce2Ru4Mg17 and a Group-Subgroup Scheme for La9Ru4In5 and Ce9Ru4Ga5

2012 ◽  
Vol 67 (3) ◽  
pp. 219-225 ◽  
Author(s):  
Stefan Linsinger ◽  
Rolf-Dieter Hoffmann ◽  
Matthias Eul ◽  
Rainer Pöttgen
Keyword(s):  
Magnetic Ordering ◽  
Direct Consequence ◽  
Structure Type ◽  
Magnetic Susceptibility Data ◽  
Space Group ◽  
Susceptibility Data ◽  
Structural Distortions ◽  
Subgroup Scheme ◽  
Tetravalent Cerium ◽  
Intermediate Valent

Ce2Ru4Mg17 was synthesized by high-frequency melting of the elements in a sealed tantalum ampoule. This magnesium-rich compound crystallizes with a new tetragonal structure type: I4̄2m, a = 986.75(8), c = 1008.7(1) pm, wR2 = 0.0513, 909 F2 values and 34 variables. The striking structural motifs in the Ce2Ru4Mg17 structure are slightly bent CeRu2 units with short Ce-Ru distances of 231 pm and additionally a short Ce-Ce distance of 307 pm. These features are a direct consequence of the cerium valence. The CeRu2 units are embedded in a magnesium-rich matrix with a broad range of Mg-Mg distances (291 - 361 pm). Temperature-dependent magnetic susceptibility data show intermediate-valent behavior of the cerium atoms (0.23(5) μB per Ce atom) and no magnetic ordering down to 3 K, indicative of almost tetravalent cerium in Ce2Ru4Mg17. The ceriumrich gallide Ce9Ru4Ga5 shows an unusually short Ce-Ru distance of 237 pm for the Ce2 position as a result of an intermediate cerium valence. The structural distortions are discussed on the basis of a group-subgroup scheme for La9Ru4In5 (space group I4/mmm) and the superstructure variant Ce9Ru4Ga5 (space group I4mm).

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