Protrait

Ruggero Frison

 

Research interest

Structural dynamics, disorder and physical properties

I investigate how materials are ordered on the atomic scale, how they grow and how their physical properties change with lowering or raising the temperature, pressure or applying magnetic or electric fields. The final goal is to find and understand the organizing principles that govern physical properties in the presence of complex disorder, which is a first step toward the design of novel materials.

X-Ray Diffraction and Scattering: experiments and modelling.

Correlated defects are responsible for the functional properties of many materials for different kinds of applications: from sensors for new medical technologies to information- or energy-storage. X-Ray Diffraction and Scattering techniques, as k-space probes, provide essential information about short-range order in crystalline lattices, systems in between order and disorder and amorphous materials.

Current research endeavors in the field of X-Ray Scattering methodology focusses on two main topics:
  • Total Scattering from Nanocrystalline and Amorphous Materials (LINK)

The diffraction pattern of a nanocrystalline powders usually display broad peaks emerging from a high and modulated background. Extracting reliable information about the structure, chemical composition, domain size and shape requires taking into account also the broad diffuse contribution underneath the Bragg peaks and, possibly, also the small-angle scattering component.

The Debye Scattering Equation (DSE) provides the spherical average of the coherent differential cross-section of the sample intrinsic scattering, that is the total scattering intensity, without any assumption about order and periodicity of the structure. Through the accurate calculation and optimization of the DSE it is possible to retrieve a "bottom-up" structural model taking into account also the size and shape effects. It is also possible to derive the atomic pair distribution function (PDF) and thus extract information about the local structure.

The computer program DebUsSy (Debye User System) consists of a suite of programs implementing a fast approach to the Debye Scattering Equation (DSE) Analysis for powder diffraction data from nanocrystalline and/or non-ordered materials. See J. Appl. Cryst. 2015, 48, 2026-2032

 

  • Diffuse Scattering in Single Crystals (LINK)

Using high quality datasets it is possible to analyse the diffuse scattering component and extract statistically reliable data from the atomic pair correlation functions: that is about the deviations from the average periodic structure of the crystalline lattice, identify the various types of disorder and derive an abstract model of interatomic vectors. By means of Monte Carlo  simulations it is possible then to build and optimize large model crystals providing a specific atomistic disorder model, whose Fourier transform fits to the experimental diffuse scattering.

Projects are running on different kinds of materials: light-conversion phosphors, multi-ferroics, superconductors, molecular solids (like MOFs) and metallic alloys.

The program ZODS (Zurich Oak Ridge Disorder Simulation) is an expandable, easy-to-use, High Performance Computing program which can run both on desktop and clusters specifically designed to address this kind of problems

Memberships in national and international organizations
  • Member of the European Physical Society

  • Member of the Swiss Physical Society

  • Member of the European Crystallographic Association

  • Member of the Swiss Crystallographic Society