Two phonon absorption in ferroelectric sodium nitrite

G D Holah

Research output: Contribution to journalArticle

Abstract

The temperature dependence of the infrared absorption spectrum of NaNO 2 has been studied in the spectral range 700 cm-1-2000 cm-1. The absorption bands in this region are due to summation and difference bands of the internal vibrations of the NO2- radical with various lattice modes. Due to the high frequencies of the internal modes these combination bands are not swamped by one or two phonon lattice mode absorption. This has made it possible to tentatively assign frequency values for various lattice phonons at points away from q approximately 0 in the Brillouin zone. Combination bands also enable longitudinal optic and transverse and longitudinal acoustic modes to be assigned. An anomalous mode has been observed at temperatures greater than 373 K whose strength is highly temperature dependent but whose frequency is essentially constant at 240 cm-1. The origin of this mode is discussed in terms of a change in the force constants between the ions due to the onset of the order-disorder ferroelectric transitions.

Original languageEnglish
Article number032
Pages (from-to)2191-2201
Number of pages11
JournalJournal of Physics C: Solid State Physics
Volume4
Issue number14
DOIs
Publication statusPublished - 1971

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nitrites
sodium
absorption spectra
Brillouin zones
infrared absorption
phonons
infrared spectra
disorders
optics
vibration
temperature dependence
temperature
acoustics
ions

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title = "Two phonon absorption in ferroelectric sodium nitrite",
abstract = "The temperature dependence of the infrared absorption spectrum of NaNO 2 has been studied in the spectral range 700 cm-1-2000 cm-1. The absorption bands in this region are due to summation and difference bands of the internal vibrations of the NO2- radical with various lattice modes. Due to the high frequencies of the internal modes these combination bands are not swamped by one or two phonon lattice mode absorption. This has made it possible to tentatively assign frequency values for various lattice phonons at points away from q approximately 0 in the Brillouin zone. Combination bands also enable longitudinal optic and transverse and longitudinal acoustic modes to be assigned. An anomalous mode has been observed at temperatures greater than 373 K whose strength is highly temperature dependent but whose frequency is essentially constant at 240 cm-1. The origin of this mode is discussed in terms of a change in the force constants between the ions due to the onset of the order-disorder ferroelectric transitions.",
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Two phonon absorption in ferroelectric sodium nitrite. / Holah, G D.

In: Journal of Physics C: Solid State Physics, Vol. 4, No. 14, 032, 1971, p. 2191-2201.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Two phonon absorption in ferroelectric sodium nitrite

AU - Holah, G D

PY - 1971

Y1 - 1971

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AB - The temperature dependence of the infrared absorption spectrum of NaNO 2 has been studied in the spectral range 700 cm-1-2000 cm-1. The absorption bands in this region are due to summation and difference bands of the internal vibrations of the NO2- radical with various lattice modes. Due to the high frequencies of the internal modes these combination bands are not swamped by one or two phonon lattice mode absorption. This has made it possible to tentatively assign frequency values for various lattice phonons at points away from q approximately 0 in the Brillouin zone. Combination bands also enable longitudinal optic and transverse and longitudinal acoustic modes to be assigned. An anomalous mode has been observed at temperatures greater than 373 K whose strength is highly temperature dependent but whose frequency is essentially constant at 240 cm-1. The origin of this mode is discussed in terms of a change in the force constants between the ions due to the onset of the order-disorder ferroelectric transitions.

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