Misfit layer compounds : Structures and physical properties

Chalcogenide misfit layer compounds

The introduction of 3d transition metals (M) into the van der Waals gaps between the weakly coupled layers of transition metal dichalcogenides TX2 (T:transition metal, X:chalcogen) produces an interesting family of intercalation compounds, M x TX2, the physical properties of which are different from those of the host TX2 matrix because of ‘host-guest’ interactions. In this article we shall review the salient features of the M x TiS2 family with the simple 1T-CdI2 type layered structure, which have been extensively studied by structural, transport, specific heat and lattice dynamic, magnetic and photoemission spectroscopic measurements. In contrast with the previously reported series of intercalation complexes of the Group V transition metal dichalcogenides, a characteristic of the M x TiS2 materials is strong hybridisation between the guest atom M 3d orbitals and the host Ti 3d and S 3p orbitals, leading to changes in the Fermi energy E F of the conduction band, the density of states at E F and v...

The electronic and magnetic properties of the 3d transition metal intercalates of TiS2

Magnetic properties of intercalation compounds MxTiS2 (M = 3d transition metal)

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS2-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS2 sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor.

https://www.mdpi.com/1996-1944/8/3/1124/pdf

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides.

The temperature dependence of electrical resistivity and thermoelectric power of the intercalation compounds of MxTiS2 (M = Mn, Fe, Co, and Ni; 0 ≦ x ≦ 1/3) with layered structures are measured over the temperature range 1.5 to 300 K. These experimental results can be explained by a simple model, which takes into account a temperature-independent residual term and intra- and intervalley scattering by acoustic phonons. It is also shown that a phonon drag effect is effective for the thermopower. The effect of intercalation of 3d metals into TiS2 layers on the electronic properties is discussed.



Die Temperaturabhangigkeit des elektrischen Widerstands und der Thermospannung der Interkalate von MxTiS2 (M = Mn, Fe, Co, und Ni; 0 ≦ x ≦ 1/3) mit Schichtstrukturen werden bei Temperaturen von 1,5 bis 300 K gemessen. Die experimentellen Ergebnisse konnen durch ein einfaches Modell erklart werden, das einen temperaturunabhangigen Restterm sowie „intra- und intervalley scattering” durch akustische Phononen berucksichtigt. Es wird auch gezeigt, das ein „phonon-drag”-Effekt fur die Thermospannung wirksam ist. Der Einflus der Interkalation von 3d-Metallen in die TiS2-Schichten auf die elektronischen Eigenschaften wird diskutiert.

Electrical Resistivity and Thermoelectric Power of Intercalation Compounds MxTiS2 (M = Mn, Fe, Co, and Ni)

The a- and c-axis resistivities and Hall coefficients of self-intercalated IT-CdI2, type layered crystals of TiS2, are measured over the temperature range 1.5 to 300 K. The temperature dependence of the carrier concentration at low temperatures T < 150 K can be explained by a simple model which takes into account both, the host Ti 3d conduction band and a localized impurity level Ei due to excess Ti atom. The position of Ei is found to lie by about 5 meV above the Fermi energy. The self-intercalated Ti atoms become ionized impurity scattering centers as Ti4+ and Ti3+ ions, whose relaxation times are calculated to give a good fit to the observed residual resistivity vs. carrier concentration curve.



Die spezifischen a- und c-Achsen-Widerstande und Hallkoeffizienten der selbstinterkalierten IT-CdJ2-Schichtkristalle von TiS2 werden bei Temperaturen von 1,5 bis 300 K gemessen. Die Temperaturabhangigkeit der Elektronendichten bei tiefen Temperaturen T < 150 K kann durch ein einfaches Modell erklart werden, das sowohl das Ti 3d-Leitungsband als auch ein lokalisiertes Storstellen-Niveau Ei infolge von uberschussigen Ti-Atomen berucksichtigt; Ei liegt etwa 5 meV oberhalb des Fermi-Niveaus. Die selbstinterkalierten Ti-Atome werden zu ionisierten Streuzentren als Ti4+ -und Ti3+-Ionen, deren berechnete Relaxationszeiten gut mit den gemessenen Restwiderstand-Ladungstragerdichte-Kurven ubereinstimmen.

Localized Impurity Level and Carrier Concentration in Self-Intercalated TiS2 Crystals

Electrical resistivities ϱ and lattice parameters of quasi-two-dimensional crystals of monoclinic η-Mo4O11 and orthorhombic γ-Mo4O11 are measured under hydrostatic pressure up to 1.2 GPa at room temperature. Both crystals have negative pressure coefficients of ϱ, which can be qualitatively explained by a phonon stiffening effect. In particular, the pressure dependence of ϱ for γ-Mo4O11 shows a drastic drop or jump at Pc = 0.3 GPa, whose magnitude and the pressure coefficients are strongly dependent on the sample resistivity or degree of stoichiometry. It is suggested that the change of a small amount of MoO4 tetrahedra into MoO6 octahedra induced by excess oxygen atoms is responsible for such structure-sensitive properties.



Bei Zimmertemperatur und hydrostatischen Drucken bis zu 1,2 GPa werden die elektrischen Widerstande ϱ und Gitterparameter von quasizweidimensionalen Kristallen von monoklinen η-Mo4O11 und rhombischen γ-Mo4O11 gemessen. Beide Kristalle haben negative Druckkoeffizienten von ϱ, die qualitativ durch einen Phononenversteifungseffekt erklart werden konnen. Insbesondere zeigt die Druckabhangigkeit von ϱ fur γ-Mo4O11 einen drastischen Abfall oder Sprung bei Pc = 0,3 GPa, dessen Grose und die Druckkoeffizienten stark von dem Probenwiderstand oder Grad der Stoichiometrie abhangig sind. Es wird angenommen, das die Anderung eines geringen Anteils von MoO4-Tetraedern in MoO6-Oktaedern, die durch uberschussige Sauerstoffatome induziert wird, fur solche strukturempfindlichen Eigenschaften verantwortlich ist.

Effect of Pressure on Electrical Resistivity and Crystal Structure of Quasi-Two-Dimensional Mo4O11

Electrical resistivities of intercalation compounds of MxTiS2 (M = Mn, Fe, Co, and Ni; x = 0.05) with the 1T-CdI2-type layered structure are measured under hydrostatic pressure up to 15 × 108 Pa over the temperature range 1.7 to 300 K. The resistivity change with pressure at room temperature and the temperature dependence at constant pressure are strongly dependent on the guest 3d metals. These experimental results can be explained by taking account of the pressure dependences of the residual resistivity, as well as the temperature-dependent intra- and intervalley scatterings by acoustic phonons.



Der elektrische Widerstand der Interkalate von MxTiS2 (M = Mn, Fe, Co, und Ni; x = 0,05) mit 1T-CdJ2-Schichtstrukturen werden unter hydrostatischen Drucken bis 15 × 108Pa bei Temperaturen von 1,7 bis 300 K gemessen. Die Widerstandsanderung mit dem Druck bei Zimmertemperatur und die Temperaturabhangigkeit unter konstantem Druck sind stark abhangig vom 3d-Gastmetall. Diese experimentellen Ergebnisse konnen unter Berucksichtigung der Druckabhangigkeit des Restwiderstands sowie der temperaturabhangigen „Intra- und Intervalley”-Streuung durch akustische Phononen erklart werden.

M. Koyano

Papers

Electrical Resistivity and Thermoelectric Power of Intercalation Compounds MxTiS2 (M = Mn, Fe, Co, and Ni)

Localized Impurity Level and Carrier Concentration in Self-Intercalated TiS2 Crystals

Effect of Pressure on Electrical Resistivity and Crystal Structure of Quasi-Two-Dimensional Mo4O11

Pressure Dependence of Electrical Resistivity in Intercalation Compounds MxTiS2 (M = 3d Transition Metal)