Observation of Lattice Parameter Changes in Silicide Powders Using an Infrared Heating High-temperature Attachment

Introduction

Lattice parameters are constants that define the size and shape of a unit cell, which is the fundamental repeating building block of a crystal structure. They consist of the unit-cell edge lengths (a, b, and c ) and the angles between them (α, β, and γ ). Lattice parameters can be refined from the peak positions of experimental powder X-ray diffraction profiles. Such refinement makes it possible to investigate subtle changes in the lattice parameters of metals and ceramics under different temperature conditions or with varying solid-solution compositions. The Reactor X high-temperature heating attachment utilizes infrared heating, allowing rapid heating rates. The use of a fused quartz sample holder makes it suitable for the measurement of materials that may react with conventional metal sample holders.

Measurement and results

Figure 1 shows the X-ray diffraction profiles of nickel silicide (NiSi) powder measured at temperatures ranging from room temperature to 1000 °C. As the temperature increases, the diffraction peaks shift either toward lower or higher angles. A shift toward lower diffraction angles indicates an increase in the lattice plane spacing (d-value). Since the direction and magnitude of the peak shifts vary among the reflections, it is expected that the thermal expansion coefficients of NiSi lattice parameters a, b, and c differ from one another, and that one of these coefficients may be negative.

Figure 2 shows the lattice parameters a, b, and c, determined by the Whole Powder Pattern Fitting (WPPF) method, as a function of measurement temperature. The angles α, β, and γ were fixed at 90° by symmetry. This result revealed that the thermal expansion of a, b, and c is anisotropic, and that the thermal expansion coefficient of b is negative. It also showed that, although the thermal expansion exhibited a gradual nonlinear dependence on temperature, the unit-cell volume increased linearly.

Fig.1: XRD profiles of NiSi powder measured at each temperature

Fig.2: Temperature dependence of the lattice parameters a, b, and c, and the unit-cell volume of NiSi

Recommended equipment and software

• SmartLab automated multipurpose X-ray diffractometer + Reactor X high-temperature attachment for reactive gases
• SmartLab Studio II integrated X-ray analysis software (Powder XRD plugin)