Ammonium halides NH₄Cl, NH₄F, and NH₄Br

Abstract

PACS 72.60.+g, 81.40Vw The resistance of ammonium chloride (NH 4 Cl), fluoride (NH 4 F) and bromide (NH 4 Br) is investigated at pressures from 20 to 50 GPa in the temperature range 77 -400 K. The transition from high-resistance to low-resistance state was found at pressures of about 15 GPa for NH 4 Br, 27 GPa for NH 4 Cl, and 42 GPa for NH 4 F, respectively. The characteristic temperature and pressure of the transition are shown to depend on the duration of the pressure treatment. All the ammonium halides show metal-like behaviour under high pressures similar to that of alkali halides. The non-monotonic temperature dependence of the resistivity, which disappears after sufficiently long pressure treatment, indicates the existence of intermediate states.

Resistivity relaxation of ammonium halides near high‐pressure induced phase transitions

“…The estimation of pressure was proved previously at extensive studies of different materials in a wide range of temperatures and pressures [3,10]. (For more details, see [8]. ) 3 General features of the resistance of ammonium halides under high pressures…”

“…Below 42 GPa, a reversible transition from low-resistive state (kOhms) to high-resistive state (more than 100 MΩ) is observed independent of previous treatment by pressure. (For more details, see [8]. )…”

“…5 and 6 of Ref. [8]). Below that temperature, the resistance has an activation character, while at higher temperatures the temperature coefficient of resistance is positive, i.e., one observes a "semiconductor-metal" transition [11].…”

“…At the beginning of our investigations, the conductivity of ammonium halides under high pressure was practically not studied. Systematic studies of conductivity these materials at high pressure were started in our works [8]. The study of material conductivity and other transport phenomena gives the simple and suitable way to discover and investigate different phase transitions induced by high pressures.…”

λ‐transition of NH4Cl and ND4Cl at high pressures

“…Also, for the λ-phase transitions in ammonium halides, particularly, in NH 4 Cl measurements of heat capacity have been reported [21][22][23][24]. Under high pressures, the structure of ammonium halides (NH 4 Cl, NH 4 Br and NH 4 F) has been studied [25,26] and recently, transport measurements have been performed for ammonium halides, in particular for NH 4 Cl to detect the phase transitions [27,28].…”