The thermal evolution of the crystal structure and phase transitions of KNbO3 were investigated by high-temperature powder X-ray diffraction and Rietveld refinement of the diffraction data. Two phase transitions from orthorhombic (Amm2) to tetragonal (P4mm) and from tetragonal to cubic (Pm3 ̅m) were confirmed, both on heating and cooling. Both phase transtions are first order based on the observed hysteresis. The mixed displacive and order-disorder nature of the tetragonal to cubic transition is argued based on symmetry and apparent divergence of the atomic positions from pseudo-cubic values. The transition between the orthorhombic and tetragonal phase show no temperature-dependence for atomic positions and only thermal expansion of the unit cell parameters and is thus discussed in relation to a lattice dynamical instability.
heating1_100-200c_60min
X-ray diffraction data in .raw format compatible with Bruker software.
heating2_210-650c_60min
X-ray diffraction data in .raw format compatible with Bruker software.
cooling1_640-150c_60min
X-ray diffraction data in .raw format compatible with Bruker software.
cooling2_140-40c_60min
X-ray diffraction data in .raw format compatible with Bruker software.
start_19-60deg_60min
X-ray diffraction data in .raw format compatible with Bruker software.
end_19-60deg_60min
X-ray diffraction data in .raw format compatible with Bruker software.
Temperature calibration with alumina
Spreadsheet used to find the real temperature as a function of set point temperature by using the thermal expansion of alumina.
T_cal_13_Mai_2016.xlsx
Refinement_parameters_Amm2_cooling
Table of all refinement parameters for the Amm2 phase of KNbO3 upon cooling. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.
Amm2_Nbfix_Bfix2_SDref_cooling.txt
Refinement_parameters_Amm2_heating
Table of all refinement parameters for the Amm2 phase of KNbO3 upon heating. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.
Amm2_Nbfix_Bfix2_SDref_heating.txt
Refinement_parameters_P4mm_cooling
Table of all refinement parameters for the P4mm phase of KNbO3 upon cooling. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.
P4mm_Nbfix_Bfix2_SDref_cooling.txt
P4mm_Nbfix_Bfix2_SDref_heating
Table of all refinement parameters for the P4mm phase of KNbO3 upon heating. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.
Refinement_parameters_Pm3m_cooling
Table of all refinement parameters for the Pm-3m phase of KNbO3 upon cooling. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.
Pm3m_Bfix2_SDref_cooling.txt
Pm3m_Bfix2_SDref_heating
Table of all refinement parameters for the Pm-3m phase of KNbO3 upon heating. Setpoint temperature can be converted to real temperature by using the temperature calibration file in the same repository.