Ukrainian Journal of Physical Optics 

Volume 22, Issue 4, 2021
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Temperature behaviour of fundamental absorption edge in superionic Ag6PS5I crystals

1Studenyak I. P., 1Pop M. M., 1Shender I. O., 1Pogodin A. I. and 2Kranjcec M. 

1Uzhhorod National University, 46 Pidhirna Street, 88000 Uzhhorod, Ukraine. studenyak@dr.com 
2North University, 33 J. Križanića Street, 42000 Varazdin, Croatia mladen. kranjcec@yahoo.com

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Abstract. Ag6PS5I single crystals are grown from solution–melt by means of a vertical zone crystallization method. Dispersion of the refractive index of Ag6PS5I measured with a spectral ellipsometry technique is described by a known Wemple–DiDomenico relation. The fundamental absorption edge for the Ag6PS5I crystals is studied in the temperature range 77–300 K. The temperature dependences of the optical pseudogap and the Urbach energy are analyzed in the framework of Einstein model. The parameters of electron–phonon interaction, which results in the Urbach behaviour of the fundamental absorption edge, are determined. The influence of temperature and structural disorderings on the optical absorption in Ag6PS5I is studied.

Keywords: superionic conductors, crystal growth, spectral ellipsometry, fundamental absorption edge, structural disorder

UDC: 535.343
Ukr. J. Phys. Opt. 22 216-224
doi: 10.3116/16091833/22/4/216/2021
Received: 27.09.2021

Анотація. Монокристали Ag6PS5I вирощено з розчину–розплаву за методом кристалізації у вертикальній зоні. Дисперсія показника заломлення Ag6PS5I, виміряна за методом спектральної еліпсометрії, описується відомим співвідношенням Вемпла–ДіДоменіко. Досліджено фундаментальний край поглинання кристалів Ag6PS5I у діапазоні температур 77–300 К. Температурні залежності оптичної псевдощілини та енергії Урбаха проаналізовано в рамках моделі Ейнштейна. Визначено параметри електрон–фононної взаємодії, що приводить до урбахівської поведінки фундаментального краю поглинання. Досліджено вплив температурних і структурних розупорядкувань на оптичне поглинання в Ag6PS5I.

Ключові слова: суперіонні провідники, ріст кристалів, спектральна еліпсометрія, край фундаментального поглинання, структурне розупорядкування
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