Combinatorial (Ba,Sr)TiO3 thin film growth: X-ray diffraction and Raman spectroscopy

Abstract

We report the investigation of the (Ba,Sr)TiO3 (BST) system of technological importance for microwave applications. The development of the combinatorial method enabled us to grow and study a library of samples ranging from BaTiO3 to SrTiO3 (ST) deposited on MgO substrate. The spatial control of the stoichiometry and of the structure has been evidenced and probed using energy dispersive x-ray spectroscopy, high resolution x-ray diffraction, and Raman spectroscopy. A global and coherent picture emerged from the complex interplay between the epitaxial/thermal stress and stoichiometry changes. Taking into account elastic interactions with the substrate we present subtle symmetry changes in the BST library in comparison with the bulk phase diagram such as tetragonal distortion observed on the ST side. Finally underdamped soft mode hardening and polar modes are detected on the high barium and strontium compositions, respectively, highlighting fundamental dynamical/structural differences with their bulk counterparts.

Stoichiometry Calculation in BaxSr1−xTiO3 Solid Solution Thin Films, Prepared by RF Cosputtering, Using X-Ray Diffraction Peak Positions and Boltzmann Sigmoidal Modelling

“…This point 59 W in the BTO magnetron corresponds to an value around 0.5. Above > 0.5 the tetragonal phase of Ba x Sr 1−x TiO 3 is reported [9,14,23], in accordance with the X-ray diffractograms in Figure 2.…”

“…It is known that ferroelectric and optical properties of BST-SS are stoichiometry dependent, for example, the electrical resistance, hysteresis cycle, and resistive switching [1], extinction coefficient and refraction index [2], the relative dielectric constant, breakdown strength, and energy density of multifunctional fibers [3], and the remanent polarization [4]. BST-SS usually crystallizes in a cubic lattice changing its lattice parameter between (Å) = 4.0577 and (Å) = 3.936 associated with the extreme compositions: BaTiO substitution in the Ba x Sr 1−x TiO 3 solid solution leads to a lattice contraction, reflected in the shift of Bragg angles, as reported in BST materials prepared by diverse techniques such as arc discharge [5], sol-gel [6][7][8] pulsed laser deposition [7], hydrothermal reaction [9], and chemical synthesis [10]. As much as both titanates are miscible in each other, the peak shift is linear and continuous between the extreme compositions; that is, it follows Vegard's law.…”

Effects of thermal processing and iron doping in co-sputtered barium strontium titanate thin films

“…4) show characteristic broad vibrational bands in the phononic region below 800 cm -1 [30]. The factor group analysis of cubic BST with m-3m (O h ) symmetry does not provide any Raman active modes.…”

Combinatorial synthesis and screening of (Ba,Sr)(Ti,Mn)O3 thin films for optimization of tunable co-planar waveguides

“…Electrically tunable barium strontium titanate (BaxSr1-xTiO3) perovskite films, hereafter referred as BSTO, of the general stoichiometry ABO3 (A and B cations of different sizes) are of strong interest due to their appealing electrical properties. [1][2][3][4] As the films possess high relative permittivity r, low loss tangent BSTO investigated for dynamic random access memory (DRAM), 5 high voltage capacitors, 6 tunable filters 7 , microwave phase shifters 8,9 etc. Although semiconductors, liquid crystals, optical fibers, magnets, ceramics and ceramic nanocomposites 10 and many other alternative materials have been used for tunable devices, ferroelectrics in their paraelectric phase are far more effective, as they exhibit high dissipation factor (Q), consume negligible power, operate at high speeds and can be tuned with relatively low DC bias (<30 V).…”