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PhD positions

Caloric and mulicaloric effects in ferroic materials

 

In the last decades, the need for more efficient and environmentally friendly cooling techniques alternative to gas compression methods has considerably increased the research efforts in the caloric effects in the solid state. Such effects refer to adiabatic temperature changes or isothermal entropy changes undergone by the materials when applying or removing external fields and may become giant close to phase transitions.

Nowadays, research has been focused mainly on the magnetocaloric and electrocaloric effects. However, they are limited by the large magnitude of magnetic fields and relatively small breakdown electric fields. Barocaloric effects (BCE), i.e. caloric effects under hydrostatic pressure, have been little explored and only in ferromagnetic alloys. Instead, BCE in ferroelectrics has not been explored yet. In particular, ferroelectric salts are good candidates to exhibit large BCE due to the presence of first-order transitions accompanied by significant volume changes. Examples are barium titanate, strontium titanate, ammonium sulfate, sodium nitrite, etc. Other promising ferroelectrics are novel metal-organic alloys.

 

Historically, the research carried out by our Group is focused on the BCE, which results in the publication of papers in high-impact journals (APL 92, 012515 (2008), Nat. Mater. 9, 478 (2010), Nature Commun. 2, 595 (2011)). In addition, the recent acquisition by the Group of a new high-pressure cell enables the simultaneous application of pressure and electric fields. The collaboration between these external fields, mediated by the coupling of different physical magnitudes and the consequent cross response, is expected to lead to the enhancement of the resulting multicaloric effects, and to the possibility of tuning the properties needed for technological application, such as good reproducibility, sharp transitions, small hysteresis, high temperature-field dependence, etc.

 

Goals: Measurement of multicaloric effects under simultaneous electric and pressure fields. Determination of materials suitability for technological application. The different used experimental techniques are Differential Scanning Calorimetry, Differential Thermal Analysis under pressure and electric field and diffraction experiments.

 

Candidates must hold the bachelor's degree in Physics or Materials Science. Interested students should contact Prof. Josep Lluis Tamarit at: josep.lluis.tamarit@upc.edu. The availability of funding is subject to obtaining a pre-doctoral grant from the PhD student. For more information see: http://www.ctt.upc.edu/Grants_118_en.html

Structure and dynamics of molecular disordered materials



Introduction
In his PhD thesis Albert Einstein connected the macroscopic description of a liquid with the microscopic movement of its molecules at long times. However his theory was not able to explain why the viscosity of some liquids increases so much that they seem to be solids at the human time scale. One example of such a liquid is window glass that a room temperature has the characteristic viscosity of a solid being its molecules disordered as in a liquid.We can find examples of such liquids in rubbers, in many foods such as candy, in rewritable CD’s, and even in some frogs that avoid freezing to death in winter. However, in spite of the great efforts of many scientists, there is no theory able to explain nowadays all the features of such liquids. Our research group is devoted to develop both experiments and molecular models to explain both the dynamics and the structure of disordered systems such as those liquids.

 


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Goal
The goal of the proposed research is to understand both the dynamics and the structure of disordered molecular systems.
Techniques
  • Neutron Diffraction
  • Quasielastic Neutron Scattering
  • Dielectric Spectroscopy
  • Molecular dynamics simulation
Previous work by our team

  • Structure:JNCS 353, 999 (2007); PRB 76, 134203 (2007)
  • Dynamics: PRL 103, 075701 (2009); PRB 81, 092202 (2010)

Fullerene-based molecular materials for (opto)electronic devices & lithium batteries

Grup de Caracterització de Materials (GCM) & Grup de Recerca en Micro i Nanotecnologies (MNT) (@ Centre de Recerca en NanoEnginyeria & ETSEIB (UPC, Barcelona))


Discovered only two decades ago, fullerene molecules, and in particular C60, have become a standard system to explore molecular matter thanks to their extremely rich behaviour which includes order-disorder transitions, molecular magnetism, and superconductivity. Fullerene-based materials have interesting charge conduction properties that are very promising for opto-electronic applications,1 as well as ionic mobility higher than standard ionic conductors,2,3 suggesting a possible application as electrode materials in alkali-ion batteries.4,5 The mechanism beyond transport phenomena is still debated, and in particular the observation of metallic-like behaviour and superconductivity is surprising, since most other organic materials behave as semiconductors.

For more information click here
fullerene