High-precision measurement of non-stoichiometry and chemical expansion of thin praseodymium-Cer mixed oxide films at high temperatures

Mohammadrasoul Alizadeh, M.Sc.

This research was funded as part of the DFG project "High-Precision Measurement of Non-Stoichiometry and Chemical Expansion of Thin Praseodymium-Cerium Mixed Oxide Films at High Temperatures" (project number 404875250).

Motivation

• Previous measurements on PCO (Praseodymium-Cerium Oxide) films yielded novel results at very low frequencies (in the millihertz range).
• During measurements in a furnace at 600 °C, it was observed that:
  • The measurement and reference beams were approximately 25 mm apart.
  • This separation led to a loss of correlation between disturbances in the two beams above 0.1 Hz.
  • As a result, turbulence-induced disturbances could no longer be effectively suppressed and were even amplified.
• To overcome this problem:
  • The new approach focuses on overlapping the beams as much as possible.
  • A stronger focus ensures that the beams remain combined over most of their path and only separate shortly before reaching the sample.
  • This is expected to improve measurement quality, especially under challenging environmental conditions and at higher frequencies.

Objective

• Development of a scanning confocal differential laser Doppler vibrometry (D-LDV) system with:
  • A large working distance.
  • Reference and measurement beams that overlap almost completely to maintain correlated disturbances and improve noise suppression.
• Enabling differential measurement of 3D vibration spectra and modes through:
  • Use of two differential measurement beams.
  • Combination of amplitude modulation (AM) and frequency modulation (FM) demodulation techniques.
• Achieving more accurate and comprehensive characterization of dynamic behavior over a wide frequency range (Up to 30 MHz).

Methode

• Integration of a confocal microscope with the D-LDV system to:
  • Precisely align the reference and measurement beams for maximum overlap.
  • Strongly focus the beams on the sample surface so that separation only occurs shortly before contact.
• Use of green laser light:
  • Taking advantage of the shorter wavelength to achieve higher spatial resolution.
• Scanning multiple measurement points:
  • Capturing vibrations in three spatial directions (3D).
  • Applying combined AM and FM demodulation to reconstruct complex vibration spectra and modes.