Istraživanje dinamike rešetke u stroncijevom titanatu

master's thesis

• Title (english): Investigation of lattice dynamics in strontium titanate
• Author: Noah Somun
• Mentor: Damjan Pelc (mentor)
• Committee member: Damjan Pelc (predsjednik povjerenstva)
• Committee member: Denis Sunko (član povjerenstva)
• Committee member: Mario Novak (član povjerenstva)
• Committee member: Miroslav Požek (član povjerenstva)
• Committee member: Ivan Kupčić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2023-09-01, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovome radu istražujemo dinamiku rešetke nedopiranog i dopiranog (metalnog) stroncijevog titanata pomoću neelastičnog raspršenja hladnih neutrona, tijekom in situ elastične deformacije. Stroncijev titanat je kvantni paraelektrik, no primjenom naprezanja može doći do feroelektričnog uređenja. Korištena je posebno dizajnirana uniaksijalna tlačna ćelija za preciznu primjenu elastičnog naprezanja na uzorak, kako bismo proučili polarni meki mod oko točke prijelaza iz paraelektrične u feroelektričnu fazu. Neutronskim raspršenjem analizirana je disperzija mekog transverzalnog optičkog (TO) moda oko centra Brillouinove zone i njena ovisnost o primijenjenom naprezanju. U nedopiranom uzorku nije vidljiva promjena moda s naprezanjem iako je očekivano njegovo omekšavanje. U dopiranom uzorku je očekivano slično ponašanje zbog niskog dopiranja, no uočeno je povećanje frekvencije moda s naprezanjem. Diskutiramo moguće uzroke neočekivanih rezultata (manjak rezolucije, nedovoljno naprezanje, fazni prijelaz prvog reda, nagnutost kristalne rešetke) i buduća mjerenja koja bi trebala pružiti objašnjenje.

Abstract (english)

In this study we investigate lattice dynamics of undoped and doped (metallic) strontium titanate using inelastic cold neutron scattering, with in situ elastic defor mation. Strontium titanate is a quantum paraelectric, but with the application of stress, it can undergo a transition to a ferroelectric phase. A specially designed uni axial strain cell was used for precise application of elastic stress to the sample, to study the polar soft mode around the paraelectric-ferroelectric transition point. The dispersion of the soft transverse optical (TO) mode from the center of the Brillouin zone and its dependence on the applied stress were analyzed by neutron scattering. In the undoped sample, no change in mode with stress is visible, although its softening is expected. In the doped sample, similar behavior is expected due to low doping; however, it was found that the mode frequency increases with stress. We discuss possible causes of unexpected results (lack of resolution, insufficient stress, first-order phase transition, lattice tilt) and future measurements that should provide an explanation.

• Keywords: stroncijev titanat; kvantni paraelektrik; dinamika rešetke; neelastično raspršenje; tlačna ćelija
• Keywords (english): strontium titanate; quantum paraelectric; lattice dynamics; inelastic scattering; pressure cell
• Language: croatian
• URN:NBN: urn:nbn:hr:217:210638
• Project: Number: UIP-2020-02-9494; Title: Kolektivna pobuđenja i lokalna struktura u nekonvencionalnim supravodičima; Title: Collective excitations and local structure of unconventional superconductors; Acronym: CELUS; Leader: Damjan Pelc; Jurisdiction: Croatia; Funder: HRZZ; Funding stream: UIP
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2025-11-24
• Created on: 2023-11-23 11:00:50