M.Sc. Physics
http://hdl.handle.net/10464/2250
2024-03-18T15:16:48ZOptical Study of (Nb0.5In0.5)0.02 Ti0.98O2 Crystals
http://hdl.handle.net/10464/15430
Optical Study of (Nb0.5In0.5)0.02 Ti0.98O2 Crystals
Cosco, Mike
This work was a study of pure TiO2Rutile crystals, as well as Rutile crystals 2% co-doped with Indium and Niobium (2-NITO). There is much interest surrounding co-doped TiO2re-cently, with several papers published on ’colossal permittivity’ in the lower frequency ranges (10^2-10^6Hz range). The aim of this work was to study the optical and Raman modes of pure and co-doped crystals to determine the effects co-doping has on these modes. Infrared reflectance along with Raman Spectroscopy were used for this purpose. In order to determine the dielectric function from the infrared data, the Factorized Model and Kramers-Kronig analysis were used. Since TiO2has a tetragonal unit cell, infrared measurements of both the a and c axes of both doped and undoped crystals were done. Thea-axis is known to have 3 optical modes, whereas the c-axis only has one. However an additional mode was seen in all spectra, believed to be caused by anharmonicity. In addition, the 136cm−1mode observed in polycrystalline conductivity spectra of 5 and 10-NITO lines up directly with the A2u mode and the 793cm−1 mode also appears in single crystal TiO2, meaning these are not new modes. However the 447cm−1 and 654cm−1 modes do not appear in our data, and are likely a result of higher percentage co-doping. The effect of co-doping was observed to be an overall decrease in the reflectance of TiO2. We also observed sizable increases inγtofor all modes in 2-NITO. In addition, the dielectric permittivity decreases below the first phonon mode; suggesting that the enhanced permittivity observed at lower frequencies is not caused by co-doped changes to phonon modes. All expected Raman-active modes were observed, however due to poor data resolution some of the peak positions appear to be slightly different than previously measured. Our Raman spectra showed new structures at around 300cm−1and 700cm−1 in the (100) surface spectra, it is possible these are combination lines.
High Temperature Method Of Measuring Electrical And Magnetic Properties Of Europium Doped Nickel Oxide
http://hdl.handle.net/10464/14867
High Temperature Method Of Measuring Electrical And Magnetic Properties Of Europium Doped Nickel Oxide
Torabi, S. Parisa
The measurement of the magnetic moment of materials as a function of temperature in
modern AC or DC magnetometers normally has a limited high temperature range up
to 400 K. To overcome this problem one needs to design ovens which can handle high
temperatures. The highest Curie temperature observed in materials is in pure Co which is
about 1400 K. However, most materials and compounds show Tc below 800 K. My thesis
research topic is to study the substitution of Ni ions by rare earth ions in NiO. The
NiO is a semiconductor which exhibits antiferromagnetism below 520 K, which makes
it suitable for applications; to name a few, rechargeable batteries, and p-type transport
conducting lms. In this study, Ni ions were substituted by 2, 5, and 8 percent of Eu ions.
The effect of substitution on the semiconducting properties of Ni1-xEuxO was studied
as function of temperature from room temperature to 1000 K. To study the magnetic
properties and the effect of Eu substitution on the Neel temperature of Ni1-xEuxO we
adapted two ovens for high temperature measurements of AC susceptibility by using the
ac modulation technique implementing a lock-in ampli er and the DC susceptibility using
the SQUID magnetometer. To check the reliability of these two ovens we also examined
the ferromagnetic transition temperatures of Bismuth Ferrite samples as function of Co
substitutions for Fe.
Electronic and Magnetic Properties of MAX Phase (Cr1-xGdx)2AlC and Er3AlC Alloy
http://hdl.handle.net/10464/14858
Electronic and Magnetic Properties of MAX Phase (Cr1-xGdx)2AlC and Er3AlC Alloy
Albandri, Huriyyah A
Bulk samples of (Cr1-xGdx)2AlC with X = 0, 0.0025, 0.01, 0.025, 0.05 and Er3AlC compound were synthesized using the arc melting technique. The samples were characterized by X-ray diffraction, magnetic susceptibility, and four probe resistivity measurements to study their magnetic and electronic properties. Using Rietveld analysis for X-ray diffraction, it was determined that the parent compound Cr2AlC exhibits a side phase of Cr7C3. The substituted samples were found to have secondary phases of Cr7C3 and GdCr3.5Al8.5 which slightly increase on increasing substitution of Cr3+ by Gd3+. The change of the concentration of Gadolinium does not have any real effect on the lattice parameter of (Cr1-xGdx)2AlC. Er3AlC contains secondary phases of ErAl2 and ErC0.6. The MAX phase Cr2AlC and the Gadolinium substituted samples show complex magnetic behaviour. The magnetization measurements show that Cr2AlC has an unusual magnetic behavior above 70 K which does not obey the Curie-Weiss law. The sample with X = 0.0025 also does not obey the Curie-Weiss law at high temperature. The susceptibility data shows that samples with X = 0.01, 0.025, and 0.05 obey the Curie-Weiss law, and the magnitude of the effective magnetic moments decreases while increasing the value of X. The susceptibility data of Er3AlC obey the Curie-Weiss law; and the effective moment is 9.1 ± 0.005 𝛍B. The resistivity measurement of the parent sample Cr2AlC indicates metallic behavior. In the Gd-substituted samples, we observed a Kondo Effect from the resistivity data. The resistivity of Gd-substituted samples increases with increasing Gadolinium concentration. We also observed metallic behavior in the Er3AlC resistivity.
Resistivity of Single Crystal Molybdenum Dioxide
http://hdl.handle.net/10464/14834
Resistivity of Single Crystal Molybdenum Dioxide
BAUER, KURTIS
The chemical vapour transport method was used to grow molybdenum oxide single crystals
so that their electrical properties could be analyzed. Satisfactory single crystal samples of
MoO2 and Mo4O11 were grown successfully using I2 as a transport agent. Crystal growths
using TeCl4 as a transport agent were also performed, though with mixed results. This
approach yielded MoO2, MoO3, and Mo9O26, but this produced samples of a quality not
suitable for single crystal analysis. Measurements performed on these samples yielded
unique results, due to their mixed oxide nature, but as the composition of each sample
was inconsistent, even between crystals from the same growth, little can be said about
them definitively. Rubidium doped single crystal growths were also attempted, to build
on previous polycrystalline Rb doped sample research, however no growths successfully
included measurable amounts of Rb. While resistivity and heat capacity measurements
performed on MoO2 did identify a phase transition in the area of 267K reported by other
researchers, there was however no evidence found to support a reported 220K electronic
transition [1]. In Mo4O11 two previously identified 109K and 30K charge density wave
transitions were observed in the DC resistivity. When AC resistivity measurements were
performed the 30K transition was not apparent. Instead, a divergence of the cooling and
warming curves not seen in the DC experiments occurred above 200K, with previously
unseen peaks appearing at 285K and 250K when cooling from 400K.