Seminar INFLPR
Miercuri, 29 Martie 2017, ora 10:30
Sectia Laseri, Sala de seminar
Titlu: „Yielding multifunctionality of laser processed thin films/nanostructures through chemical pressure and epitaxial strain”
Prezinta: Dr. Nicu Scarisoreanu
Rezumat: Perovskite, lead-free materials have become very attractive lately for a broad range of applications such as photovoltaic, photocatalytic, electronics and so on. Exhibiting a wide range of functional properties, ranging from normal ferroelectrics up to relaxor ferroelectrics by varying the amount of A-site and/or B-site substitutions in the perovskite systems, bulk lead free perovskites are intensively studied. Nonetheless, to transpose bulk properties to thin films is a major achievement.This is the case of case of perovskite materials with small band gap values such as bismuth ferrite (BiFeO3- BFO) which have become very attractive for photovoltaic and photocatalytic applications. BFO exhibit both ferroelectric and ferromagnetic properties with a high remnant ferroelectric polarization (95 μC/cm2) and Curie temperature (Tc~1103 K). The band gap value of BiFeO3 (Eg~2.71 eV) corresponding to maximum absorptivity at visible wavelengths and, if doped with Yttrium or Lanthanum, the band gap value can be decreased even lower. BiFeO3 is by far the most promising and investigated multiferroic material but it has two major drawbacks: low dielectric susceptibility and high dielectric loss.
Recently, we have underlined how a critically important material for eco-friendly (Pb-free) multiferroic multifunctional devices can be tailored, by joining doping and epitaxial strain engineering to create a nanoscale stripe structure, in order to overcome its major drawback namely the low dielectric response. By high resolution transmission electron microscopy (HR-TEM) and geometric phase analysis (GPA) we have evidenced nanostripe domains with alternating compressive and tensile strain in the Y-doped BiFeO3 epitaxial thin films. Dielectric constant behavior for undoped samples is presented in the same frequency and temperature conditions and it is clearly lower than for doped samples, which points to the joined role of doping and epitaxial strain for the enhancement of dielectric constant, due to easy response of nanodomains to electrical stimulus.
Another example of how the strain engineering in thin films approach can be applied for growing thin films with enhanced the dielectric and piezoelectric responses, is for the case of (Ba1−xCax)(ZryTi1−y)O3 (BCZT) materials. Our recent studies have demonstrated the possibility to obtain lead-free (Ba1−xCax)(ZryTi1−y)O3 (BCZT) thin films with very high dielectric permittivity and piezoelectric coefficients [1, 2]. Epitaxial thin films of BCTZ have been deposited on single-crystalline substrates with different lattice parameters (SrTiO3, SrLaAlO4, LaAlO3, GdScO3) substrates by pulsed laser deposition. The high dielectric permittivity of BCZT thin films was attributed, besides to their high structural quality, to the enhanced susceptibility of the nanoscale domain configuration to a small external perturbation. The enhanced switching of such nanodomain configuration was probed by piezoforce microscopy, and values up to 230 pm/V has been obtained for d33 piezoelectric coefficients.
[1] F. Cordero, F. Craciun, M. Dinescu, N. Scarisoreanu, C. Galassi, W. Schranz, and V. Soprunyuk, Appl. Phys. Lett. 105, 232904 (2014).
[2] N. D. Scarisoreanu, F. Craciun, A. Moldovan, V. Ion, R Birjega, C. Ghica, R. F. Negre, M. Dinescu, ACS Appl. Mater. Interfaces, 7, 23984−23992 (2015).
[3] N. D. Scarisoreanu, F. Craciun, R. Birjega, V. Ion, V. Teodorescu, C. Ghica, R. Negrea, M. Dinescu, Scientific Reports, Nature Publishing Group, (6), 25535-25535 (2016).
