Related Experiment Video
Updated: Aug 7, 2026
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Glasslike two-level systems in minimally disordered mixed crystals
J P Wrubel1, B E Hubbard, N I Agladze
1Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853-2501, USA.
Physical Review Letters
|June 29, 2006
Summary
Terahertz (THz) spectroscopy revealed two-level systems in mixed crystals like BaCaF2 and PbCaF2. This previously unknown behavior emerges at specific calcium fluoride concentrations, suggesting collective dopant tunneling.
Area of Science:
- Solid-state physics
- Materials science
- Spectroscopy
Background:
- Glasses exhibit two-level systems (TLS) due to disorder.
- Substitutional monatomic mixed crystals offer minimally disordered systems for study.
- The presence of TLS in such systems was previously unknown.
Purpose of the Study:
- To investigate the presence and origin of two-level systems in Ba(1-x)Ca(x)F2 and Pb(1-x)Ca(x)F2 mixed crystals.
- To understand the concentration dependence of TLS emergence.
- To elucidate the underlying mechanism responsible for TLS in these systems.
Main Methods:
- Terahertz (THz) spectroscopy was employed to probe the systems.
- Analysis of the concentration dependence of observed phenomena.
- Modeling using the statistics of impurity distribution within the crystal lattice.
Main Results:
- A broad distribution of two-level systems, characteristic of glasses, was identified.
- Two-level behavior was observed to initiate at a specific CaF2 concentration in these minimally disordered systems.
- The concentration dependence of TLS was successfully modeled, aligning with impurity distribution statistics.
Conclusions:
- The study demonstrates the occurrence of glass-like two-level systems in specific mixed crystal compositions.
- A collective dopant tunneling mechanism is proposed as the cause for the observed two-level behavior.
- This finding expands the understanding of disorder-induced phenomena in crystalline solids.
Related Concept Videos
02:37Metallic Solids
Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability. Many...
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability. Many...
02:22Structures of Solids
Solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern are known as crystalline solids. Metals and ionic compounds typically form ordered, crystalline solids. A crystalline solid has a precise melting temperature because each atom or molecule of the same type is held in place with the same forces or energy. Amorphous solids or non-crystalline solids (or, sometimes, glasses) which lack an ordered internal structure and are randomly arranged. Substances that...
02:42Ionic Crystal Structures
Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
01:24The Seven Crystal Systems: Overview
Crystals with various point group symmetries belong to different crystal classes, which are synonymous terms. Despite being in the same class, crystals may have distinct shapes, like cubes and octahedra. There are 32 three-dimensional point groups, all of which are systematically divided into seven crystal systems.The basic cubic crystal system, exemplified by NaCl, features orthogonal vectors (α = β = �� = 90°) of equal lengths (a = b = c). When specific requirements are not imposed on the...
01:25Imperfections in Crystal Structure: Point, Line and Plane Defects
A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...
01:18Unit Cells
A crystal's internal structure is an orderly array of atoms, ions, or molecules, and the details of this array significantly influence the solid's properties. In a crystal, periodically repeating 'structural motifs' - which could be atoms, molecules, or groups thereof - create a 'space lattice.' This is essentially a three-dimensional, infinite array of points, each surrounded by its neighbors in an identical way, forming the basic structure of the crystal.A 'unit cell' is a theoretical...