Ukrainian Journal of Physical Optics 

Volume 22, Issue 4, 2021

Home page

Other articles 

in this issue
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. 
2North University, 33 J. Križanića Street, 42000 Varazdin, Croatia mladen.

Download this article

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.

  1. Ohno S, Banik A, Dewald G F, Kraft M A, Krauskopf T, Minafra N, Till P, Weiss M and Zeier W G, 2020. Materials design of ionic conductors for solid state batteries. Progr. Energy. 2: 022001. doi:10.1088/2516-1083/ab73dd
  2. Grey C P and Hall D S, 2020. Prospects for lithium-ion batteries and beyond - a 2030 vision. Nature Commun. 11: 6279. doi:10.1038/s41467-020-19991-4
  3. Sun Y-K, 2020. Promising all-solid-state batteries for future electric vehicles. ACS Energy Lett. 5: 3221-3223. doi:10.1021/acsenergylett.0c01977
  4. He X, Zhu Y and Mo Y, 2017. Origin of fast ion diffusion in super-ionic conductors. Nature Commun. 8: 15893. doi:10.1038/ncomms15893
  5. Kuhs W F, Nitsche R and Scheunemann K, 1979. The argyrodites - a new family of tetrahedrally close-packed structures. Mat. Res. Bull. 14: 241-248. doi:10.1016/0025-5408(79)90125-9
  6. Nilges T and Pfitzner A, 2005. A structural differentiation of quaternary copper argyrodites: Structure - property relations of high temperature ion conductors. Z. Kristallogr. 220: 281-294. doi:10.1524/zkri.
  7. Zhou L, Assoud A, Zhang Q, Wu X and Nazar L F, 2019. New Family of argyrodite thioantimonate lithium superionic conductors. J. Amer. Chem. Soc. 141: 19002-19013. doi:10.1021/jacs.9b08357
  8. Studenyak I P, Stefanovich V O, Kranjcec M, Desnica D I, Azhnyuk Yu M, Kovacs Gy Sh and Panko V V, 1997. Raman scattering studies of Cu6PS5Hal (Hal = Cl, Br, I) fast-ion conductors. Solid State Ionics. 95: 221-225. doi:10.1016/S0167-2738(96)00477-8
  9. Beeken R B, Garbe J J, Gillis J M, Petersen N R, Podoll B W and Stoneman M R, 2005. Electrical conductivities of the Ag6PS5X and the Cu6PSe5X (X = Br, I) argyrodites. J. Phys. Chem. Solids. 66: 882-886. doi:10.1016/j.jpcs.2004.10.010
  10. Pogodin A I, Filep M J, Malakhovska T O, Sabov M Yu, Sidey V I, Kokhan O P and Studenyak I P, 2019. The copper argyrodites Cu7−nPS6−nBrn: crystal growth, structures and ionic conductivity. Solid State Ionics. 341: 115023. doi:10.1016/j.ssi.2019.115023
  11. Hanghofer I, Brinek M, Eisbacher S L, Bitschnau B, Volck M, Hennige V, Hanzu I, Rettenwander D and Wilkening H M R, 2019. Substitutional disorder: structure and ion dynamics of the argyrodites Li6PS5Cl, Li6PS5Br and Li6PS5I. Phys. Chem. Chem. Phys. 21: 8489-8507. doi:10.1039/C9CP00664H
  12. Orliukas A F, Kazakevicius E, Kezionis A, Salkus T, Studenyak I P, Buchuk R Yu, Prits I P and Panko V V, 2009. Preparation, electric conductivity and dielectrical properties of Cu6PS5I-based superionic composites. Solid State Ionics. 180: 183-186. doi:10.1016/j.ssi.2008.12.005
  13. Studenyak I P, Izai V Yu, Studenyak V I, Kovalchuk O V, Kovalchuk T M, Kopčanský P, Timko M, Tomašovičová N, Zavisova V, Miskuf J and Oleinikova I V, 2017. Influence of Cu6PS5І superionic nanoparticles on the dielectric properties of 6СВ liquid crystal. Liq. Cryst. 44: 897-903. doi:10.1080/02678292.2016.1254288
  14. Šalkus T, Kazakevičius E, Banys J, Kranjčec M, Chomolyak M M, Neimet Yu Yu and Studenyak I P, 2014. Influence of grain size effect on electrical properties of Cu6PS5I superionic ceramics. Solid State Ionics. 262: 597-600. doi:10.1016/j.ssi.2013.10.040
  15. Studenyak I P, Kranjčec M, Izai V Yu, Chomolyak A A, Vorohta M, Matolin V, Cserhati C and Kökényesi S, 2012. Structural and temperature-related disordering studies of Cu6PS5I amorphous thin films. Thin Solid Films. 520: 1729-1733. doi:10.1016/j.tsf.2011.08.043
  16. Studenyak I P and Kranjčec M. Disordering Effects in Superionic Conductors with Adgyrodite Structure. Uzhhorod: Hoverla (2007).
  17. Studenyak I P, Buchuk R Yu, Bendak A V, Yamkovy O O, Kazakevicius E, Salkus T, Kezionis A and Orliukas A F, 2014. Electric conductivity studies of composites based on (Cu1−xAgx)6PS5I superionic conductors. SPQEO. 17: 425-428. doi:10.15407/spqeo17.04.425
  18. Azzam R M A and Bashara N M. Ellipsometry and Polarized Light. Amsterdam: North-Holland Publishing Company (1977).
  19. Studenyak I P, Kranjcec M, Kovacs Gy S, Panko V V, Desnica I D, Slivka A G and Guranich P P, 1999. The effect of temperature and pressure on the optical absorption edge in Cu6PS5X (X= Cl, Br, I) crystals. J. Phys. Chem. Solids. 60: 1897−1904. doi:10.1016/S0022-3697(99)00220-6
  20. Wemple S H and Di Domenico M, 1971. Behaviour of the dielectric constant in covalent and ionic materials. Phys. Rev. B. 3: 1338−1352. doi:10.1103/PhysRevB.3.1338
  21. Tubbs M S, 1970. A spectroscopic interpretation of crystalline ionicity. Phys. Stat. Sol. (b). 41: K61−K64. doi:10.1002/pssb.19700410164
  22. Urbach F, 1953. The long-wavelength edge of photographic sensitivity and electronic absorption of solids. Phys. Rev. 92: 1324−1326. doi:10.1103/PhysRev.92.1324
  23. Kurik M V, 1971. Urbach rule (review). Phys. Stat. Sol. (a) 8: 9−30. doi:10.1002/pssa.2210080102
  24. Sumi H and Sumi A, 1987. The Urbach−Martiensen rule revisited. J. Phys. Soc. Jap. 56: 2211-2220. doi:10.1143/JPSJ.56.2211
  25. Sumi H and Toyozawa Y, 1971. Urbach−Martiensen rule and exciton trapped momentarily by lattice vibrations. J. Phys. Soc. Jap. 31: 342−357. doi:10.1143/JPSJ.31.342
  26. Dow J D and Redfield D, 1972. Toward a unified theory of Urbach's rule and exponential absorption edge. Phys. Rev. B. 5: 594−610. doi:10.1103/PhysRevB.5.594
  27. Samuel L, Brada Y, Burger A and Roth M, 1987. Urbach rule in mixed single crystals of ZnxCd1−xSe. Phys. Rev. B. 36: 1168−1173. doi:10.1103/PhysRevB.36.1168
  28. Beaudoin M, DeVries A J G, Johnson S R, Laman H and Tiedje T, 1997. Optical absorption edge of semi-insulating GaAs and InP at high temperatures. Appl. Phys. Lett. 70: 3540−3542. doi:10.1063/1.119226
  29. Yang Z, Homewood K P, Finney M S, Harry M A and Reeson K J, 1995. Optical absorption study of ion beam synthesized polycrystalline semiconducting FeSi2. J. Appl. Phys. 78: 1958−1963. doi:10.1063/1.360167
  30. Cody G D, Tiedje T, Abeles B and Brooks B, Goldstein Y, 1981. Disorder and the optical-absorption edge of hydrogenated amorphus silicon. Phys. Rev. Lett. 47: 1480−1483. doi:10.1103/PhysRevLett.47.1480
(c) Ukrainian Journal of Physical Optics