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Electronic and optical properties of lead iodide
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
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2002 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, s. 7219-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.

Ort, förlag, år, upplaga, sidor
2002. Vol. 92, s. 7219-
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:uu:diva-92018DOI: 10.1063/1.1523145OAI: oai:DiVA.org:uu-92018DiVA, id: diva2:164953
Tillgänglig från: 2004-09-01 Skapad: 2004-09-01 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Ingår i avhandling
1. Density Functional Theory in Computational Materials Science
Öppna denna publikation i ny flik eller fönster >>Density Functional Theory in Computational Materials Science
2004 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The present thesis is concerned to the application of first-principles self-consistent total-energy calculations within the density functional theory on different topics in materials science.

Crystallographic phase-transitions under high-pressure has been study for TiO2, FeI2, Fe3O4, Ti, the heavy alkali metals Cs and Rb, and C3N4. A new high-pressure polymorph of TiO2 has been discovered, this new polymorph has an orthorhombic OI (Pbca) crystal structure, which is predicted theoretically for the pressure range 50 to 100 GPa. Also, the crystal structures of Cs and Rb metals have been studied under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs-III and Rb-III phases. Thus, it is now certain that the famous isostructural phase transition in Cs is rather a new crystallographic phase transition.

The elastic properties of the new superconductor MgB2 and Al-doped MgB2 have been investigated. Values of all independent elastic constants (c11, c12, c13, c33, and c55) as well as bulk moduli in the a and c directions (Ba and Bc respectively) are predicted. Our analysis suggests that the high anisotropy of the calculated elastic moduli is a strong indication that MgB2 should be rather brittle. Al doping decreases the elastic anisotropy of MgB2 in the a and c directions, but, it will not change the brittle behaviour of the material considerably.

The three most relevant battery properties, namely average voltage, energy density and specific energy, as well as the electronic structure of the Li/LixMPO4 systems, where M is either Fe, Mn, or Co have been calculated. The mixing between Fe and Mn in these materials is also examined. Our calculated values for these properties are in good agreement with recent experimental values. Further insight is gained from the electronic density of states of these materials, through which conclusions about the physical properties of the various phases are made.

The electronic and magnetic properties of the dilute magnetic semiconductor Mn-doped ZnO has been calculated. We have found that for an Mn concentration of 5.6%, the ferromagnetic configuration is energetically stable in comparison to the antiferromgnetic one. A half-metallic electronic structure is calculated by the GGA approximation, where Mn ions are in a divalent state leading to a total magnetic moment of 5 μB per Mn atom.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2004. s. 49
Serie
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1001
Nyckelord
Physics, Density Functional Theory, High Pressure, Phase Transitions, Elastic Properties, Lithium Batteries, Dilute Magnetic Semiconductors, Fysik
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:uu:diva-4496 (URN)91-554-6016-X (ISBN)
Disputation
2004-09-24, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Handledare
Tillgänglig från: 2004-09-01 Skapad: 2004-09-01 Senast uppdaterad: 2012-03-28Bibliografiskt granskad
2. Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations
Öppna denna publikation i ny flik eller fönster >>Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations
2006 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In many materials, changes in chemical composition, pressure or temperature can induce metal to insulator transitions. It is recently observed in yttrium hydride, for example, changes from a shiny mirror (YH2) to a transparent window (YH3), which has important technological application in optical devices. We have tuned the above transition by choosing pressure instead of composition. Our predicted finding is confirmed by recent experiments and opens a new way to design optical switches.

The unique role that gold plays in society is to a large extent related to the fact that it is the most noble of all metals.We have studied the noble nature of gold by choosing pressure as tool. Our prediction shows that gold transforms from a face centered cubic to an hexagonal closed packed phase above 200 GPa whereas platinum, another noble metal, does not show any phase transition up to 500 GPa. This prediction has also been confirmed by experiments suggesting that platinum is more noble than gold.

The growing concern about climate change and fossil fuel availability, the direct conversion of solar irradiation into electricity appears to be an ideal alternative to conventional energy sources. Power generation by solar cells is a direct method of solar energy conversion. We report a new cubic phase of TiO2 which can be stabilized at ambient conditions. This phase has an absorption three or four orders of magnitude larger than the conventional state-of-the-art solar cell based on anatase TiO2. Therefore, we are introducing a well established material with a new structure for future generation solar cells. The same effect is also observed in cubic SnO2.

Electronic and optical properties of other materials such as BexZn1-xTe, RuO2 and IrO2 are also studied in present thesis. In particular, for BexZn1-xTe, we have used composition as a tool to tune the optical properties.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2006. s. 51
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 192
Nyckelord
Physics, Density Functional Theory, Electronic Structure, Phase Transitions, High Pressure, Optical Properties, Dielectric Functions, Semiconductors, Metals, Fysik
Identifikatorer
urn:nbn:se:uu:diva-6923 (URN)91-554-6584-6 (ISBN)
Disputation
2006-05-26, Häggsalen, Ångström Laboratory, Uppsala, 13:15
Opponent
Handledare
Tillgänglig från: 2006-05-08 Skapad: 2006-05-08 Senast uppdaterad: 2013-08-01Bibliografiskt granskad

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