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Related Concept Videos

Phase Transitions02:31

Phase Transitions

Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to occupy...
Phase Transitions01:21

Phase Transitions

A phase transition is the process in which a substance changes from one state of matter to another, like from a solid to a liquid, liquid to gas, or vice versa, at a specific temperature and under given pressure conditions. This change is spontaneous and is affected by alterations in temperature and pressure. These parameters impact the strength of the forces between molecules (intermolecular forces) in the substance.During a phase transition, both the initial and final phases of the substance...
Phase Diagram01:19

Phase Diagram

The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).
Phase Diagram01:24

Phase Diagram

A phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure. It shows the boundaries between solid, liquid, and gas phases and the conditions at which these phases coexist in equilibrium. An area in a phase diagram represents a single phase, whereas lines or phase boundaries represent the equilibrium between two phases.In the phase diagram of water, the boundary line between the solid and liquid states illustrates...
Phase Diagrams02:39

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points). Regions or areas labeled solid, liquid, and gas represent single phases, while lines or curves represent...
Phase Changes01:19

Phase Changes

Phase transitions play an important theoretical and practical role in the study of heat flow. In melting or fusion, a solid turns into a liquid; the opposite process is freezing. In evaporation, a liquid turns into a gas; the opposite process is condensation.
A substance melts or freezes at a temperature called its melting point and boils or condenses at its boiling point. These temperatures depend on pressure. High pressure favors the denser form of the substance, so typically, high pressure...

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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
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Pressure-induced phase transitions in LiNH2.

Raja S Chellappa1, Dhanesh Chandra, Maddury Somayazulu

  • 1Materials Science & Engineering Division, Department of Chemical & Metallurgical Engineering (MS 388), University of Nevada, Reno, Nevada 89557, USA. rchellappa@ciw.edu

The Journal of Physical Chemistry. B
|August 23, 2007
PubMed
Summary

High-pressure Raman spectroscopy revealed a reversible phase transition in lithium amide (LiNH2) starting around 12 GPa. This transition leads to a new phase with ordered amide ions, observed up to 25 GPa.

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Area of Science:

  • Materials Science
  • Solid-State Chemistry
  • Spectroscopy

Background:

  • Lithium amide (LiNH2) is a material with potential applications in hydrogen storage and as a solid-state electrolyte.
  • Understanding its structural behavior under pressure is crucial for optimizing its properties.

Purpose of the Study:

  • To investigate the high-pressure phase behavior of lithium amide (LiNH2) using in situ Raman spectroscopy.
  • To identify pressure-induced phase transitions and characterize the structural changes.

Main Methods:

  • In situ high-pressure Raman spectroscopy was employed.
  • Measurements were conducted on LiNH2 at pressures up to 25 GPa.

Main Results:

  • A reversible phase transition was observed, initiating around 12 GPa and completing by 14 GPa.
  • The transition is from the ambient alpha-LiNH2 phase to a high-pressure beta-LiNH2 phase.
  • Spectroscopic analysis indicated orientational ordering of [NH2]- ions in the beta-LiNH2 phase.

Conclusions:

  • Lithium amide undergoes a pressure-induced phase transition to a structurally distinct phase at high pressures.
  • The observed spectral changes, including N-H stretching modes and lattice mode behavior, are consistent with orientational ordering of the amide ion.