Vibrational dynamics and phase diagram of KNbO3 up to 30G Pa and from 20 to 500K

International audienceD ow n lo a de d B y : [B IU S J u s s ie The phase diagramof KNbO3 was investigatedby Ramanscattering upto 30GPaandfrom10to500K(750Kat 2GPa). Macroscopic ferroelectricity vanishes on compressionand the various ferroelectric solids, rhombohedral, orthorhombicandtetragonal (R–O–T), werefoundtoexist inclosedomainsof thepressure–temperatureplane.SpecificallytheTsolidvanishesbelow200Kand theRandOsolidsexist, verylikely, downto0K. Quantumsuppressionof the Rsolidlikelyoccursbelow100K.Thetransitiontothecubicparaelectricphaseis ofthedisplacivetypeatlowtemperaturewhereasitisoftheorder–disordertype athightemperature. Inthecubicsolid, first-orderRamanscattering, assignedto structural distortionduetodynamical disorder, wasobserved. Thedistortionis orthorhombicbelow200Kandtetragonalabove,whichmaystemfromtherapid decreasewithtemperatureof theNbiondwellingtimeinitsallowedsites