NMR and birefringence study of structural transitions in disordered crystals: Rb/sub x/K/sub 1-x/MnF/sub 3/

Journal Article · Sat Jan 01 00:00:00 EST 1977 · Phys. Rev., B; (United States)

DOI:https://doi.org/10.1103/PhysRevB.15.84· OSTI ID:7133740

Borsa, F; Benard, D J; Walker, W C; Baviera, A

Measurements of /sup 39/K and /sup 87/Rb NMR and of modulated birefringence have been performed in Rb/sub x/K/sub 1-x/Mnf/sub 3/ mixed single crystals (x = 0.02, 0.04, 0.06, 0.1, 0.15, 0.27) in the temperature range 60--300 K. It was found that the structural phase transition which occurs at 184 K in pure KMnF/sub 3/ is moved towards lower temperatures upon substitution of K with Rb. The approximate law valid for x up to 0.15 is T/sub c/(x) = T/sub c/(0)(1 - 2x) approx. = T/sub c/(0)(1 - x)/sup 2/. The result is discussed in terms of the cation effect on the stability of the cubic perovskite structure. The rotation angle phi of the MnF/sub 6/ octahedra appears to remain the order parameter with the average rotation angle decreasing as x increases. The NMR results indicate in addition that for x > or = 0.02, phi becomes nonuniform over distances of a few lattice spacings. A distribution of phi having a rms width of about 7.5% of the average phi is found for the sample x = 0.02. The birefringence results indicate that the first-order discontinuity at T/sub c/ is still present for x = 0.02 and 0.04 but is rounded off for x > or = 0.06. This result is interpreted in terms of a spatial distribution of transition temperatures due to the statistical fluctuations in concentration within ''correlation volumes.'' (AIP)

• Research Organization: Ames Laboratory-U.S. ERDA and Department of Physics, Iowa State University, Ames, Iowa
• OSTI ID: 7133740
• Journal Information: Phys. Rev., B; (United States), Vol. 15:1
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MANGANESE FLUORIDES
CRYSTAL-PHASE TRANSFORMATIONS
REFRACTION
POTASSIUM 39
NUCLEAR MAGNETIC RESONANCE
POTASSIUM FLUORIDES
RUBIDIUM 87
RUBIDIUM FLUORIDES
LOW TEMPERATURE
MEDIUM TEMPERATURE
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MANGANESE COMPOUNDS
MANGANESE HALIDES
NUCLEI
ODD-EVEN NUCLEI
PHASE TRANSFORMATIONS
POTASSIUM COMPOUNDS
POTASSIUM ISOTOPES
RADIOISOTOPES
RESONANCE
RUBIDIUM COMPOUNDS
RUBIDIUM ISOTOPES
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
YEARS LIVING RADIOISOTOPES
360603* - Materials- Properties