Other techniques

2.10.1 Solid state NMR

Solid state NMR was used to probe the local structure of specific nuclei to determine the local structure of a material. It gives information on a number of nearest neighbours, level of disorder and may show the presence of defects in the local structure.

Solid state NMR was performed at the University of St. Andrews by Martin Peel and Professor Sharon Ashbrook. NMR spectra were acquired using a Bruker 600 Avance III spectrometer, equipped with a wide-bore 14.1 T magnet, giving Larmor frequencies of 158.7 MHz for 23Na (I = 3/2) and 92.1 MHz for 2H (I = 1).

Powdered samples were packed into conventional 4-mm ZrO2 rotors, and a magic-

angle spinning (MAS) rate of 12.5 kHz was employed. 23Na chemical shifts were

referenced to 1 M NaCl(aq) using a secondary reference NaCl(s) (δiso = 7.8 ppm),

and 2H chemical shifts were referenced to deuterated tetramethylsilane, using the OD

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reference. Conventional 23Na and 2H MAS NMR spectra were obtained using single-

pulse experiments at 14.1 T, with typical pulse lengths of 1.5 and 4 μs, respectively. Recycle intervals of 5 and 3 s were used for 23Na and 2H, respectively, with a

radiofrequency nutation rate of ~100 kHz and ~50 kHz, respectively.

2.10.2 Transmission Electron Microscopy

Transmission Electron Microscopy (TEM) is a microscopy technique whereby a beam of highly energetic electrons is transmitted through a thin sample, interacting with the specimen as it passes through, to examine samples at a very high magnification. TEM images were obtained by Dr Reza Kashtiban, Department of Physics, University of Warwick, on a JEOL 2100 LaB6 instrument, operating at

200 kV. The sample was dispersed ultrasonically in ethanol and then deposited dropwise onto 3 mm lacey of carbon grids supplied by Agar.

2.10.3 Thermogravimetric analysis

Thermogravimetric analysis (TGA) is an analytical technique used to determine a material‟s thermal stability by monitoring the mass change that occurs when the sample is heated. This technique was used to determine the exact amount of water present in the starting materials and as-prepared materials.

TGA measurements were carried out by Luke Daniels, Department of Chemistry, University of Warwick, using a Mettler Toledo systems TGA/DSC 1-600

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instrument. Typical measurements were performed in air with a heating rate of 10 oC/min from room temperature up to1000 oC,

2.10.4 Inductively coupled plasma optical emission spectroscopy

Inductively coupled plasma optical emission spectroscopy (ICP-OES) is an analytical technique used to determine the atomic composition of materials. It is a type of emission spectroscopy that uses inductively coupled plasma to produce excited atoms and ions that emit radiation at wavelengths characteristic of a particular element. Measurements were performed by MEDAC Ltd.

2.10.5 Photocatalysis and Photoluminescence

Photocatalysis measurements were performed by measuring the H2 and O2

evolved from the breakdown of methanol when visible light and UV light (420 nm filter used) was exposed to the sample. Photocatalytic measurements were also carried out on the decomposition of methylene blue. The measurements were made by David Martin and Dr. Junwang Tang at University College London.

2.10.6 Dielectric measurements

Samples that were investigated for their dielectric properties were first pressed into a pellet of diameter 13 mm using a load of 2 tonnes. Approximately 1 g of powder was used to make each pellet. The pellets were placed on Pt foil and

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heated to 1100 oC, at a heating rate of 5 oC/min, for 2 hours. After being left to cool

to room temperature, another heating run at 1150 oC for 4 hours was carried out. The

mass, thickness and diameter of the pellets were then measured to determine their density. Silver paint was then applied on both faces of the pellet for dielectric and piezoelectric measurements.

Piezoelectricity

First, the pellets were poled by placing them in silicone oil and applying a fixed voltage for 1 minute. The longitudinal piezoelectric coefficient, d33, was then

measured at 5 different points on each sides of the pellet using a YE2730A d33 meter.

An average and standard deviation of these values was then calculated.

Dielectric hysteresis

The hysteresis measurement was performed on pellets immersed in silicone oil using a triangular waveform at a frequency of 50 mHz. The peak voltage was increased until a current peak associated with the coercive field was observed. Data were collected using Labview software.

Dielectric permittivity

The dielectric permittivity and loss of the pellets were measured at frequencies of 1 kHz, 10 kHz, 100 kHz and 1 MHz using a HP 4192 A LF Impedance Analyser at a heating rate of 60 oC h-1. The pellets were heated from 30

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2.11 References

(1) Weller, M. T. Inorganic Materials Chemistry; Oxford University Press Inc.: New York, 2008.

(2) JCPDS; International Center for Diffraction Data: PA, U.S.A, 2008

(3) Rietveld, H. M. Acta. Cryst.1967, 22, 151.

(4) Rietveld, H. M. J. Appl. Cryst.1969, 2, 65.

(5) Topas Academic technical reference

(6) Coelho, A. A.; Evans, J. S. O.; Evans, I. R.; Kern, A.; Parsons, S. Powder Diffr.

2011, 26, S22.

(7) Fernandez-Garcia, M. Cat. Rev. - Sci. Eng.2002, 44, 59.

(8) Dent, A. J.; Cibin, G.; Ramos, S.; Smith, A. D.; Scott, S. M.; Varandas, L.; Pearson, M. R.; Krumpa, N. A.; Jones, C. P.; Robbins, P. E. 14th International Conference on X-Ray Absorption Fine Structure (XAFS14), Camerino, ITALY, 2009.

(9) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem.1985, 57, 603.

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Chapter 3 – Hydrothermal Synthesis and