Impurity-Governed Modification of Optical and Structural Properties of ZrO2-Based Composites Doped with Cu and Y

Abstract

The influence of calcination temperature on copper spatial localization in Y-stabilized ZrO2 powders was studied by attenuated total reflection, diffuse reflectance, electron paramagnetic resonance, transmission electron microscopy, electron energy loss, and energy-dispersive X-ray spectroscopies. It was found that calcination temperature rise in the range of 500–700 °C caused the increase of copper concentration in the volume of ZrO2 nanocrystals. This increase was due to Cu in-diffusion from surface complexes that contained copper ions linked with either water molecules or OH groups. This copper in-diffusion led also to an enhancement of absorption band peaked at ~270 nm that was ascribed to the formation of additional oxygen vacancies in nanocrystal volume. Further increasing of calcination temperature from 800 up to 1000 °C resulted in outward Cu diffusion accompanied by a decrease of the intensity of the 270-nm absorption band (i.e., oxygen vacancies’ number), the transformation of ZrO2 tetragonal (cubic) phase to monoclinic one as well as the enhancement of absorption band of dispersed and crystalline CuO in the 600–900 nm range.

Peculiarities of Thermally Activated Migration of Subvalent Impurities in Cu-Doped Y-Stabilized ZrO2 Nanopowders Produced From Zr Oxychlorides

“…The spectrum II is observed in the samples calcined at higher temperatures (800-1,000 • C) when the contribution of spectrum I decreases. This signal is similar to that observed in the samples prepared from the nitrate raw material and can be ascribed to Cu 2+ Zr ions in monoclinic structure (Korsunska et al, 2017).…”

“…These peaks can tentatively be ascribed to the hydroxyl stretching modes of Cu 2 Cl(OH) 3 (Du et al, 2015). This assumption is confirmed by the absence of these narrow bands in the samples prepared from the nitrates (Korsunska et al, 2017). These bands are more pronounced in the Cu-1 samples (T c = 600-800 • C) while in Cu-8 samples, they are only observed for T c = 800 • C. For higher T c values, the bands related with Cu and Cl complexes vanish.…”

“…EPR spectra of studied samples are shown in Figure 6. Depending on T c values, two types of EPR spectra are present in our samples in a similar way to those obtained for samples prepared from nitrate raw materials (Korsunska et al, 2015a(Korsunska et al, , 2017. The first type (spectrum I) is observed for Cu-1 samples calcined at T c = 500-800 • C and in Cu-8 samples calcined at T c = 500-900 • C. The other kind of EPR spectrum (spectrum II) contains a set of irregular shape lines in a wide range of magnetic fields and is detected in samples calcined at higher temperatures (T c = 800-1,000 • C for Cu-1 samples and T c = 1,000 • C for Cu-8 ones) when the intensity of spectrum I decreases (Figure 6).…”

“…The absorption band near the band edge of ZrO 2 at ∼270 nm was earlier identified as light absorption by oxygen vacancies (Korsunska et al, 2017). Its intensity in Cu-1 and Cu-8 samples calcined at 500 • C does not differ notably.…”

“…At the same time, the simultaneous presence of Cu inside the grains and on their surface can be achieved by co-precipitation technique (Korsunska et al, 2014(Korsunska et al, , 2017. In this case, the variation of calcination temperature (T c ) allows Cu relocation between volume and surface of nanocrystals.…”