Book/Dissertation / PhD Thesis FZJ-2017-02366

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png
Manipulating the Structural and ElectronicProperties of Epitaxial NaNbO$_{3}$ Films via Strainand Stoichiometry



2016
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-185-9

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 136, VI, 114 S. () = Universität Köln, Diss., 2016

Please use a persistent id in citations:  

Abstract: Due to their intriguing dielectric, pyroelectric, elasto-electric, or opto-electric properties, oxide ferroelectrics are vital candidates for the fabrication of most electronics. However, these extraordinary properties exist mainly in the temperature regime around the ferroelectric phase transition, which is usually several hundreds of K away from room temperature. Therefore, the manipulation of oxide ferroelectrics, especially moving the ferroelectric transition towards room temperature, is of great interest for application and also basic research. In this thesis, we demonstrate this using examples of NaNbO$_{3}$ films. We show that the transition temperature of these films can be modified via plastic strain caused by epitaxial film growth on a structurally mismatched substrate, and this strain can be fixed by controlling the stoichiometry. The structural and electronic properties of Na$_{1+x}$NbO$_{3+δ}$ thin films are carefully examined byamong others XRD (e.g. RSM) and TEM and cryoelectronic measurements. Especially the electronic features are carefully analyzed via specially developed interdigitated electrodes in combination with integrated temperature sensor and heater. The electronic data are interpreted using existing as well as novel theories and models, they are proved to be closely correlated to the structural characteristics. The major results are:- Na$_{1+x}$NbO$_{3+δ}$ thin films can be grown epitaxially on (110)NdGaO$_{3}$ with a thickness up to 140nm (thicker films have not been studied). Plastic relaxation of the compressive strain sets in when the thickness of the film exceeds approximately 10 – 15 nm. Films with excess Na are mainly composed of NaNbO$_{3}$ with minor contribution of Na$_{3}$NbO$_{4}$. The latter phase seems to form nanoprecipitates that are homogeneously distributed in the NaNbO$_{3}$ film which helps to stabilize the film and reduce the relaxation of the strain. - For the nominally stoichiometric films, the compressive strain leads to a broad and frequency-dispersive phase transition at lower temperature (125 – 147 K). This could be either a new transition or a shift in temperature of a known transition. Considering the broadness and frequency dispersion of the transition, this is actually a transition from the dielectric state at high temperature to a relaxor-type ferroelectric state at low temperature. The latter is based on the formation of polar nano-regions (PNRs). Using the electric field dependence of the freezing temperature, allows a direct estimation of the volume (70 to270 nm$^{3}$) and diameter (5.2 to 8 nm, spherical approximation) of the PNRs. The values confirm with literature values which were measured by other technologies. [...]


Note: Universität Köln, Diss., 2016

Contributing Institute(s):
  1. Bioelektronik (PGI-8)
  2. Bioelektronik (ICS-8)
Research Program(s):
  1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2017
Database coverage:
Creative Commons Attribution CC BY 4.0 ; OpenAccess
Click to display QR Code for this record

The record appears in these collections:
Institute Collections > IBI > IBI-3
Document types > Theses > Ph.D. Theses
Document types > Books > Books
Workflow collections > Public records
ICS > ICS-8
Publications database
Open Access
PGI-8

 Record created 2017-03-24, last modified 2022-09-30