PhD Research

Investigation of the structures and physical properties of novel lead-free niobates for piezoelectric applications. The main focus of the PhD is on potassium sodium niobate (K_xNa_1-xNbO₃), both as a stand-alone material and in solid solutions with other perovskite structures, such as LiTaO₃, LiSbO₃ and BaTiO₃. KNN is of particular interest because of its high piezoelectric response and the proposed presence of several morphotropic phase boundaries.

Techniques

• X-ray Diffraction: used to determine the crystal structure and lattice parameters of the materials. Data taken on the group's Panalytical X'Pert Pro MPD with Anton Paar furnace attachment.
• Neutron Scattering: also used to determine crystal structure, particularly oxygen positions. Powder diffraction as a function of temperature will be carried out for selected compositions at ISIS, UK, and ILL, Grenoble.
• Impedance Analyser: for measurements of the dielectric susceptibility of samples at various temperatures.
  
• NMR : examines the local environments of atoms in the samples. This technique will compliment the X-ray/neutron scattering of general structure, to examine the local structure, and how it changes in the presence of a morphotropic phase boundary. The active nuclei that will be studied include ²³Na, ³⁹K, ⁹³Nb and ¹⁷O (enriched samples). All measurements will be performed on the solid-state NMR spectrometers at Warwick, with magnetic fields ranging from 4.7 - 14.1 T.
• Rietveld Refinement: Topas Academic is used to perform Pawley and rietveld refinement to determine structure, composition and thermal parameters of materials. Charge flipping will also be implemented when single crystals are available.
  
• Single Crystal Growth: Attempts are underway to produce single crystal specimens of KNN at the various morphotropic phase boundaries using the flux method. Currently small single crystals have been grown with compositions from x = 0.1 to x = 0.4.
• Single Crystal diffraction: Scans of single crystals taken with Oxford diffraction Gemini CCD diffractometer, with data analysed using Crysalis Pro and Shelx software.

 

Conferences and Workshops

10/06	Edinburgh	PCG meeting
01/07	Durham	PCG Rietveld Workshop
02/07	Liberec	Piezoelectricity for end users III	Workshop also attended
04/07	Leicester	Condensed Matter and Materials Physics	Talk given on KNN phase diagram
08/07	Marrakech	European Crystallography Meeting	Poster presented on KNN tilt system and new high temperature phase
09/07	Oxford	10th Oxford School on Neutron Scattering
08/08	Osaka	IUCr conference 2008	Poster presented on single crystal and powder work of KNN
09/10	Warsaw	E-MRS Fall meeting 2010	Oral presentation on MPBs in lead-free piezoelectrics

        

 Experiments

09/06	ISIS, UK	HRPD/GEM	Phase diagram mapping of KNN
10/07	ILL, France	D2B	Low temperature scans and MPB analysis of KNN

Published Papers

Structural study of K_xNa_1-xNbO₃ (KNN) for compositions in the range x = 0.24 - 0.36, D. W. Baker, P. A. Thomas, N. Zhang & A. M. Glazer, Acta Cryst. (2009). B65, 22-28

A comprehensive study of the phase diagram of K_xNa_1-xNbO₃, D. W. Baker, P. A. Thomas, N. Zhang & A. M. Glazer, Appl. Phys. Lett. (2009). 95, 091903

Structures of K_0.05Na_0.95NbO₃ (50-300 K) and K_0.30Na_0.70NbO₃ (100-200 K), N. Zhang, A. M. Glazer, D. Baker & P. A. Thomas, Acta Cryst. (2009). B65, 291-299

 

Supervisors

My supervisors for the PhD are Prof. Pam Thomas (Crystallography) and Prof. Mark Smith (NMR). 

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