Ruddlesden-Popper Homologous Series Research Articles

Thermoelectric properties of Srn+1TinO3n+1 (n=1, 2, 3, ∞) Ruddlesden–Popper Homologous Series

The transport properties of Srn+1TinO3n+1 (n = 1, 2, 3, ∞) Ruddlesden–Popper Homologous Series were evaluated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code. Based on the electronic band structure calculations, we have calculated the charge carrier's concentration at 300, 600 and 900 K, and found that the Sr4Ti3O10 compound exhibit the highest charge carrier's concentration along the temperature scale.We also have calculated the electrical conductivity and electronic thermal conductivity at 300, 600 and 900 K, and found that in the vicinity of Fermi level these materials exhibit the minimum value of electrical conductivity and electronic thermal conductivity, which is represent the regions where the investigated materials can give its maximum efficiency. For all compounds the highest value of Seebeck coefficient occurs at 300 K then it decreases with increasing the temperature. We have calculated the power factor (P) at 300, 600 and 900 K, and found that beyond the vicinity of Fermi level these materials exhibit the maximum value of P, which is represent the regions where the investigated materials can give its maximum efficiency. We notice that Sr2TiO4 compound exhibit figure of merit (ZT) equal to unity for p-/n-type between −0.1 and +0.05 μ(eV) at all temperatures, and Sr3Ti2O7 compound exhibit ZT equal to unity for p-/n-type between −0.1 and +0.02 μ(eV). Sr4Ti3O10 exhibit ZT equal to unity for all temperatures in the p-type region, whereas in the n-type region it exhibits a unity at 300 K, 1.1 at 600 K and 1.2 at 900 K. While SrTiO3 exhibit ZT equal to unity for p-/n-type between ∓0.1 μ(eV) at all temperatures.

Dynamic layer rearrangement during growth of layered oxide films by molecular beam epitaxy.

The A(n+1)B(n)O(3n+1) Ruddlesden-Popper homologous series offers a wide variety of functionalities including dielectric, ferroelectric, magnetic and catalytic properties. Unfortunately, the synthesis of such layered oxides has been a major challenge owing to the occurrence of growth defects that result in poor materials behaviour in the higher-order members. To understand the fundamental physics of layered oxide growth, we have developed an oxide molecular beam epitaxy system with in situ synchrotron X-ray scattering capability. We present results demonstrating that layered oxide films can dynamically rearrange during growth, leading to structures that are highly unexpected on the basis of the intended layer sequencing. Theoretical calculations indicate that rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases. We demonstrate the utility of the new-found growth strategy by performing the first atomically controlled synthesis of single-crystalline La3Ni2O7.

Effect of reduced dimensionality on the optical band gap of SrTiO3

The effect of dimensional confinement on the optical band gap of SrTiO3 is investigated by periodically introducing one extra SrO monolayer every n SrTiO3 layers. The result is the n = 1–5 and 10 members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series. Spectroscopic ellipsometry, optical transmission, and cathodoluminescence measurements reveal these Srn+1TinO3n+1 phases to have indirect optical band gaps at room temperature with values that decrease monotonically with increasing n. First-principles calculations suggest that as n increases and the TiO6 octahedra become connected for increasing distances along the c-axis, the band edge electronic states become less confined. This is responsible for the decrease in band gaps with increasing n (for finite n) among Srn+1TinO3n+1 phases.

Synthesis and magnetic properties of the complex oxide La1.5Sr1.5CuMnO6.67

A new oxide phase, La1.5Sr1.5CuMnO6.67, related to the Ruddlesden-Popper homologous series An + 1BnO3n + 1 (n = 2) was synthesized. The magnetic susceptibility of the obtained compound obeys the Curie-Weiss law above 114 K. At 14 K, a magnetic anomaly related to the transition to the spin-glass state was detected.

Electronic Band Structure and Optical Properties of Srn+1TinO3n+1 Ruddlesden–Popper Homologous Series

State-of-the-art calculations of electronic band structures, density of states and frequency-dependent optical properties have been reported for Srn+1TinO3n+1 (n=1, 2, 3, ∞) compounds. These materials possess indirect wide energy band gaps. The frequency dependent optical properties of n=1,2,3 compounds show considerable anisotropy and positive birefringence. The conduction band minimum is originates from Ti-d states, while the valence band maximum is governed by O-p states. The bandwidth of the Ti-d states is responsible for the decrease in the energy band gap as n changes from 1 to 2, 3, and ∞. We have analyzed the degree of hybridization on the basis of the ratio of the orbital overlapping within the muffin tin sphere.

Strategies To Stabilize New Oxides in the Srn+1(CoTa)nO3n+1 Ruddlesden–Popper Homologous Series

Two new oxides of the Ruddlesden-Popper series have been isolated and structurally characterized in the Sr-Co-Ta-O system. X-ray and electron diffraction and high-resolution electron microscopy show that polycrystalline Sr(3)CoTaO(7) constitutes the n=2 member of a new Sr(n+1)(CoTa)(n)O(3n+1) homologous series, the essential feature of which is the existence of two connected Co/Ta octahedral layers, separated by Sr atoms. Sr(2)CoTaO(6), the n=infinity member of the series, shows a particular short-range ordering of Co and Ta at the octahedral sites leading, as shown by high-resolution electron microscopy, to the disordered intergrowth of simple and double perovskite type domains. Strategies to stabilize new oxides of this series are discussed.

Preparation and Properties of Srn+1TinO3n+1 Ruddlesden-Popper Homologous Series by Metal-Citric Acid Complex Decomposition Method

AbstractWe investigated the Srn+1TinO3n+1 Ruddlesden-Popper homologous series. This material exhibits a wide range of electric behaviors, from a high-dielectric-constant tunable-paraelectric in its undoped form to a metallic superconductor when it is doped with a variety of elements.The Srn+1TinO3n+1 and the yttrium-doped Srn+1TinO3n+1 Ruddlesden-Popper homologous series were prepared through the thermal decomposition of a metal citric acid complex. The starting solution consisted of the raw materials strontium acetate and titanium alkoxide. Citric acid was used as the chelating agent, and ethanol and distilled water were mixed and used as a solvent. Single phase Sr2TiO4 and Sr3Ti2O7 were produced without creation of SrCO3 by heat-treatment at 1073 and 1473 K, respectively, for three hours. We were unable to produce single phase Sr4Ti3O10. The samples consisted of Sr4Ti3O10 and SrTiO3 phases. Scanning electron microscopy showed that the grain shape of the Sr2TiO4 was plate-like, while those of the Sr3Ti2O7 and Sr4Ti3O10 were not and the grains had large numbers of pores. High-density Sr2-xYxTiO4 (x= 0 to 0.06) ceramic samples were produced under hot-press conditions (1823 K for one hour at a uniaxial pressure of 31.2 MPa). Although the undoped samples were insulators, the yttrium-doped samples showed high electrical conductivity (i.e. that of Sr1.98Y0.02TiO4 was ρ= 8.5×10−5 Ωcm). The Seebeck coefficient of Sr1.98Y0.02TiO4 was –160.7 μV/K, and the thermal conductivity was 3.38 W/mK.

Stability and thermodynamic functions of lanthanum nickelates

Enthalpy of formation, entropy, and heat capacity of La 3Ni 2O 7, La 4Ni 3O 10, and LaNiO 3, which belong to the Ruddlesden-Popper homologous series were investigated using equilibration with the gas phase, adiabatic calorimetry, and differential scanning calorimetry. All three compounds remain almost stoichiometric in their stability range, while the established energetic trends are consistent with decreasing thermal stability in the order La 3Ni 2O 7 > La 4Ni 3O 10 > LaNiO 3. The enthalpy of the structural phase transition in La 3Ni 2O 7 at 490 K was determined. The derived thermodynamic functions were used to construct the phase stability diagram of the La–Ni–O system in terms of temperature and oxygen pressure.

Temperature Dependence of Microwave and THz Dielectric Response in Srn + 1TinO3n + 1 (n = 1–4)

The microwave, near-millimetre and infrared (IR) dielectric response of Srn + 1TinO3n + 1 (n = 1–4) Ruddlesden-Popper homologous series was studied in the temperature range 10 to 300 K. Remarkable softening of the polar optical mode was observed in Sr4Ti3O10 and Sr5Ti4O13 which explains the increase in microwave permittivity and dielectric loss upon cooling. However, both samples have a distinct content of SrTiO3 dispersed between SrO layers. It is proposed therefore that the observed soft mode originates from the SrTiO3 microscopic inclusions.

Composition dependence of the lattice vibrations in Srn+1TinO3n+1 Ruddlesden–Popper homologous series

Abstract Room-temperature infrared reflectivities, time-domain THz transmission spectra and micro-Raman spectra of ceramics in the Ruddlesden–Popper homologous series, Srn+1TinO3n+1 (where n=1, 2, 3, 4, ∞), were studied. Increasing the number of perovskite layers (n) in the crystal system resulted in higher polarizability of the lattice and softening of the lowest frequency phonon mode, which is responsible for the observed increase in microwave permittivity, dielectric loss and temperature coefficient of resonance frequency with n. Although the infrared and Raman spectra revealed many defects in the ceramics (e.g. second phases and stacking faults), the extrapolation of experimental submillimetre dielectric data to the microwave region showed no dielectric dispersion below the phonon frequencies and prevailingly an intrinsic origin of losses in the microwave region in almost all samples (except for Sr5Ti4O13).

Epitaxial growth of the first five members of the Srn+1TinO3n+1 Ruddlesden–Popper homologous series

The first five members of the Srn+1TinO3n+1 Ruddlesden–Popper homologous series, i.e., Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, Sr5Ti4O13, and Sr6Ti5O16, have been grown by reactive molecular beam epitaxy. A combination of atomic absorption spectroscopy and reflection high-energy electron diffraction intensity oscillations were used for the strict composition control necessary for the synthesis of these phases. X-ray diffraction and high-resolution transmission electron microscope images confirm that these films are epitaxially oriented and nearly free of intergrowths. Dielectric measurements indicate that the dielectric constant tensor coefficient ε33 increases from a minimum of 44±4 in the n=1(Sr2TiO4) film to a maximum of 263±2 in the n=∞(SrTiO3) film.

Atomic Structure Of Epitaxial Thin Films Of The Srn+1tinO3n+1 Ruddlesden-Popper Homologous Series

The n+1TinO3n+1 Ruddlesden-Popper homologous series are promising candidates in the search for low loss tunable dielectric materials. SrTiO3 (n=∞) has the perovskite structure with alternating TiO2 and SrO layers. However, those members of the n+1TinO3n+1 series with n≠∞ have tetragonal symmetry and space group 14/mmm. These phases are formed by inserting a rock-salt SrO layer every n SrTiO3 perovskites, resulting in a successive perovskite blocks being mutually sheared by [1/2,1/2,0] (Fig. 1).Previously, the n = 1 - 3 members of this series have been made in polycrystalline form using solid state synthesis methods. Attempts to synthesize intermediate members (4≤n<∞) have been unsuccessful and resulted in mixed phase samples. Fortunately, significant advancement in epitaxial growth techniques makes it possible to control the synthesis of a wide variety of homologous oxide crystal systems. In the present work, thin films of the Srn+1TinO3n+1, RP series with n = 1 - 5 have been synthesized using reactive molecular beam epitaxy (MBE).