Title page for etd-1005113-220304


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URN etd-1005113-220304
Author Chih-Hung Nien
Author's Email Address No Public.
Statistics This thesis had been viewed 5350 times. Download 1291 times.
Department Materials and Optoelectronic Science
Year 2013
Semester 1
Degree Ph.D.
Type of Document
Language zh-TW.Big5 Chinese
Title Crystal Symmetry and Phase Transition in Undoped and Ca-Doped SrTiO3 Ceramics
Date of Defense 2013-11-01
Page Count 377
Keyword
  • Phase transition
  • Crystal symmetry
  • Additive
  • Orientation relationships
  • SrTiO3
  • Abstract The crystalline phase mixture and microstructure of SrO-excess SrTiO3 powder sintered at 1350oC/4 h is analyzed using X-ray diffractometry (XRD), scanning and transmission electron microscopy (SEM and TEM). Second phases represented by Ruddlesden-Popper Sr3Ti2O7 (RP2) and Sr4Ti3O10 (RP3) coexist with SrTiO3 (ST), consistent with the SrO-TiO2 phase equilibrium diagram. Some ST grains contain inter-grown RP2 lamellae which permits analysis of the ST-RP2 interface. The ST-RP2 boundary shared by (001)ST and (001)RP2, although containing a lattice mismatch, is accommodated by long range elastic strain. The crystallographic orientation relationships of ST and RP2 at the interface are determined by selected area diffraction patterns (SADP) and described by transformation matrices. The crystallographic shear structure across the ST-RP boundary exhibiting the characteristic α-fringe pattern can be represented by a fault vector R = 1/2<111>ST.
    X-ray diffractometry (XRD) and Rietveld refinement combined with transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS) and convergent beam electron diffraction (CBED) techniques are used to analyze crystalline phases and their symmetry in Sr0.65Ca0.35TiO3 (SCT35 with x = 0.35) sintered ceramic. The tetragonal (T)- and orthorhombic (O)-phase crystalline mixture at a ratio of approximately 4:1 is found in sintered Sr0.65Ca0.35O3.
    Adopting the Buxton-Tanaka-Champness CBED procedures and examining the Gjǿnnes and Moodie (GM) lines enable determining the crystal symmetry to 4/mmm point group and I4/mcm space group for a grain with x = 0.26, and mmm point group and Pbnm space group for a grain with x = 0.31. The paraelectric C-Pm3m → antiferrodistortive T-I4/mcm → antiferroelectric O-Pbnm transition sequence for SCT upon cooling is confirmed, only that for x = 0.26 it stops at the T-phase at room temperature. The discrepancy in Ca-content is accounted for by chemical inhomogeneity in the initial powder prepared via mixed oxides route. The PE C-Pm3m → AFD T-I4/mcm → AFE O-Pbnm transition sequence for SCT upon cooling holds true, but with leaner Ca-content, e.g., x = 0.26, it only arrives at AFD T-I4/mcm.
    Advisory Committee
  • Bing-Hwait Hwang - chair
  • Yu-Chuan W - co-chair
  • Ming-Horng Lin - co-chair
  • Wei-Lin Wang - co-chair
  • Chi-Shiung Hsi - co-chair
  • Hong-Yang Lu - advisor
  • Files
  • etd-1005113-220304.pdf
  • Indicate in-campus at 1 year and off-campus access at 1 year.
    Date of Submission 2013-11-18

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