The Human Resources Strategy for Researchers

PhD Opportunity: New Materials Synthesis by Crystallisation of Glass or Melt

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    First Stage Researcher (R1)
    05/07/2019 23:59 - Europe/Brussels
    France › ORLEANS

The CEMHTI laboratory is affiliated to the CNRS and is composed of 2 sites (high temperature and cyclotron sites) regrouping about 100 people.
The laboratory develops original expertise and tools on a national and international level to study in situ the physico-chemical properties of materials under extreme conditions.
The doctoral student will be based on the laboratory's high temperature site, will integrate the Vitro) transparent ceramics and structures team and will be attached to the team leader.

Facilities and Equipment
The CEMHTI laboratory offers excellent facilities for the synthesis and characterization of ceramics and glass-ceramics including:
- Aerodynamic levitation platforms with coupled laser heating
- Powder XRD suite operating up to 2000 °C
- High-resolution Transmission Electron Microscope
- High-temperature IR and Raman spectroscopy
- High-field high-temperature solid state NMR spectroscopy

This thesis will allow the candidate to acquire expertise in the field of glass-ceramics, for the synthesis of new crystalline materials with emerging optical or ionic-transport properties. Depending on the candidate's profile, he or she may prefer an emphasis on innovative synthesis methods, powder crystallography (ab-initio structural determination) or transmission electron microscopy. The project benefits from established national and international collaborations for specific physical property measurements, advanced diffraction, and computational prediction methods.
Project Background
Solid state synthesis by crystallisation-from-glass or direct crystallisation-from-melt offers access to a range of useful and unusual inorganic materials that cannot be isolated by conventional sintering-based routes. At CEMHTI, we are using containerless aerodynamic levitation (ADL) apparatus with laser heating to synthesise precursor glasses and melts of diverse compositions, and crystallising these to produce highly dense oxide ceramics with new crystal structures and/or microstructures that host desirable physical properties for optical and ionic transport applications (http://www.cemhti.cnrs-orleans.fr/instruments/levitation.aspx).
This approach is particularly applicable to the development of transparent polycrystalline ceramics, which belong to an emerging class of photonic materials that compete with "single crystal technology" in a wide range of optical applications such as laser materials, scintillators, optical lenses and transparent armors. These new ceramics offer many advantages, including large-scale shaping and production, and tolerate higher levels of active ion doping than single crystals, which improves optical performance. In parallel, we are also using the ADL method to stabilise new highly non-stoichiometric oxides with high concentrations of interstitial oxide ion defects; such materials are of interest as electrolytes in next-generation (intermediate-temperature) solid oxide fuel cells. For both applications, we are seeking new compositions and structures (at both the unit-cell and microscopic level) to develop materials with superior properties.
Objectives and realisation
The objective of the project is to expand the range of known transparent ceramics and/or interstitial oxide ion conductors by isolating new oxides – which may be metastable – by crystallisation-from-glass or direct crystallisation-from-melt. The new materials will be characterised structurally (from the unit cell to the micro scale) and physically, to understand the link between structure and properties, allowing their performance to be optimised.
The thesis work will consist of a first experimental and methodological part that will make it possible to identify new glass compositions with either (i) congruent crystallisation that retain transparency in the visible and/or infrared regions during crystallisation, or (ii) that correspond to crystalline structure-types of interest as interstitial oxide hosts. To do this, the CEMHTI laboratory is equipped with an original synthesis method allowing the vitrification of relatively refractory compositions: aerodynamic levitation coupled with laser heating. In certain cases the method will be accelerated by identifying promising compositions computationally, in collaboration with the University of Liverpool (UK), thus increasing the efficiency of the synthetic process.
The second part of the work will focus on the structural characterisation of the ceramic materials obtained: crystallographic characterisation of the structure at the unit-cell level by X-ray, neutron and electron diffraction (which may involve ab-initio structure solution methods), and the use of electron microscopy to study the nature and morphology of the crystals, grain boundaries, or the presence of residual phases. The study of microstructure/transparency correlation during the crystallisation processes should make it possible to optimise the synthesis parameters (e.g. composition, annealing conditions) to obtain high-quality materials and improved properties. The CEMHTI laboratory has a wide range of multi-scale characterisation techniques that can be used in-situ (HTXRD, SEM, MET...) and numerous spectroscopic methods (NMR, Raman, EXAFS...) to determine the structural characteristics of the synthesised ceramics. We have strong collaborations with major synchrotron and neutron facilities, allowing us to carry out highly detailed structural characterisations. Finally, the functional ceramics obtained will be optically and mechanically characterised within the framework of collaborations.

Facilities and Equipment
The CEMHTI laboratory offers excellent facilities for the synthesis and characterization of ceramics and glass-ceramics including:
- Aerodynamic levitation platforms with coupled laser heating
- Powder XRD suite operating up to 2000 °C
- High-resolution Transmission Electron Microscope
- High-temperature IR and Raman spectroscopy
- High-field high-temperature solid state NMR spectroscopy

External Collaborations
The project will benefit from national and international collaborations with the following institutes:
- IRCP (Paris) and IMN (Nantes) : characterisation of optical properties, and PDF local structure analysis (ANR project « PERSIST »).
- IRCER (Limoges): high pressure powder sintering of glass.
- APS (Argonne - USA) synchrotron and French and European neutron sources (LLB/ESS/ILL)
- ICMS (Seville, Spain): characterisation of optical properties.
- GUT (Guilin, China): conductivity measurements by AC impedance spectroscopy.
- University of Liverpool (Liverpool, UK): calculation of stable dopants and structures.

The Candidate
In addition to project management experience, this thesis work will allow the doctoral student to acquire expertise in the field of high-performance oxide materials, including transparent ceramics with optical properties that are of great interest for major glass companies including Saint-Gobain, Corning, and Schott. The ideal candidate will have a good undergraduate degree in a relevant subject (e.g. Chemistry, Physics, Materials Science), will have completed a Masters research project in solid-state science, and will demonstrate a desire to learn more about the field.

The following publications are relevant to the project:
[1] J.Xu et al., Interstitial Oxide Ion Migration Mechanism in Aluminate Melilite La1+xCa1-xAl3O7+0.5x Ceramics Synthesized by Glass Crystallization, ACS Applied Energy Materials, 2(4), 2878-2888 (2019)
[2] X.Yang et al., Cooperative mechanisms of oxygen vacancy stabilization and migration in the isolated tetrahedral anion Scheelite structure, Nature Communications, 9, 4484 (2018)
[3] X.Ma et al., 'Pressureless glass crystallization of transparent yttrium aluminum garnet-based nanoceramics', Nature Communications, 9 1175 (2018)
[4] M.Boyer et al., 'First transparent oxide ion conducting ceramics synthesized by full crystallization from glass', J. Mater. Chem. A, 6 5276-5289 (2018)
[5] W.Wisniewski et al., 'Oriented Nucleation and Crystal Growth in SrO-Al2O3-SiO2 Tectosilicate Glasses', CrystEngComm, 20 3455-3466 (2018)
[6] A.J.Fernández-Carrión et al., Local Disorder and Tuneable Luminescence in New Sr1-x/2Al2- xSixO4 (x = 0.2, 0.4 and 0.5) Transparent Ceramics, Inorg. Chem., 56 14446-14458 (2017)
[7] M.Boyer et al., Transparent Polycrystalline SrREGa3O7 Melilite Ceramics: Potential Phosphors for Tuneable Solid State Lighting, J. Mater. Chem. C, 4 3238-3247 (2016)
[8] M. Boyer et al., Enhanced transparency through second phase crystallization in BaAl4O7 scintillating ceramics, Cryst. Growth Des., 16, 386 (2016).
[9] K.Al Saghir et al., Transparency through Structural Disorder: A New Concept for Innovative Transparent Ceramics, Chem. Mater., 27 508-514 (2015).
[10] S.Alahraché et al., Perfectly transparent Sr3Al2O6 polycrystalline ceramic elaborated from glass crystallization, Chem. Mater., 25 4017-4024 (2013).
[11] M.Allix et al., Highly Transparent BaAl4O7 Polycrystalline Ceramic Obtained by Full Crystallization from Glass, Advanced Mater., 24 5570-5575 (2012).
[12] S. Alahrache et al., brevet "Céramiques transparentes", dépôt en France N° 1161025 du 1er décembre 2011, extension internationale PCT N° EP2012/074171 du 30 novembre 2012.

Mathieu ALLIX : mathieu.allix@cnrs-orleans.fr
Mike PITCHER : michael.pitcher@cnrs-orleans.fr
CNRS - CEMHTI 1D, avenue de la recherche scientifique 45071 Orléans cedex 2, France

Additional comments

Application deadline set for 05/07/2019

Web site for additional job details

Required Research Experiences


Offer Requirements

    Chemistry: Master Degree or equivalent
    Physics: Master Degree or equivalent
    Technology: Master Degree or equivalent
    FRENCH: Basic
Work location(s)
1 position(s) available at
Conditions Extrêmes et Matériaux : Haute température et Irradiation

EURAXESS offer ID: 417263
Posting organisation offer ID: 9988


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