Helical polymer 1/∞[P2Se62-]: Strong second harmonic generation response and phase-change properties of its K and Rb salts

In Chung, Christos D. Malliakas, Joon I. Jang, Christian G. Canlas, David P. Weliky, Mercouh G. Kanatzidis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

112 Scopus citations


The selenophosphates A2P2Se6 (A = K, Rb) crystallize in the chiral trigonal space group P3121, with a = 7.2728(9) Å, c = 18.872(4) Å, and Z = 3 at 298(2) K and a = 14.4916(7) Å, c = 18.7999(17) Å, and Z = 12 at 173(2) K for K + salt and a = 7.2982(5) Å, c = 19.0019(16) Å, and Z = 3 at 100(2) K for Rb+ salt. The A2P2Se 6 feature parallel one-dimensional helical chains of 1/∞[P 2Se62-] which depict an oxidative polymerization of the ethane-like [P2Se6]4- anion. On cooling well below room temperature K2P2Se 6 exhibits a displacive phase transition to a crystallographic subgroup and forms a superstructure with a cell doubling along the a- and b-axes. The Rb analogue does not exhibit the phase transition. The compounds are air stable and show reversible glass-crystal phase-change behavior with a band gap red shift of 0.11 and 0.22 eV for K+ and Rb+ salts, respectively. Raman spectroscopy, 31P magic angle spinning solid-state NMR, and pair distribution function (PDF) analysis for crystalline and glassy K2P2Se6 give further understanding of the phase transition and the local structure of the amorphous state. K 2P2Se6 exhibits excellent mid-IR transparency and a strong second harmonic generation (SHG) response. The SHG response is type-I phase-matchable and in the wavelength range of 1000-2000 nm was measured to be 50 times larger than that of the commercially used material AgGaSe 2. Glassy K2P2Se6 also exhibits an SHG response without the application of electric field poling. In connection with the NLO properties the thermal expansion coefficients for K 2P2Se6 are reported.

Original languageEnglish (US)
Pages (from-to)14996-15006
Number of pages11
JournalJournal of the American Chemical Society
Issue number48
StatePublished - Dec 5 2007
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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