The Composition of Intermediate Products of the Thermal Decomposition of (NH4)2ZrF6 to ZrO2 from Vibrational-Spectroscopy Data

Fluoridation of HfO2

“…In the second, alternative sequence, hydrolysis of the ammonium hafnium fluoride material occurs simultaneously with loss of NH 3 and HF (at x = 1, 2, or 3 in eq ), necessarily resulting in one or more ammonium hafnium oxyfluoride intermediates. This is the reported progression of phases that occurred when (NH 4 ) 2 ZrF 6 was heated in air at a relative humidity of 20–30%, as determined by Voit and colleagues via XRD and vibrational spectroscopy . Assuming, as in the Zr case, that (NH 4 ) 4– x HfF 8– x has decomposed to the x = 3 composition before hydrolysis occurs, the equation for this step is given by …”

“…The main reaction heating profile for all mixture compositions consisted of one to three cycles of heating at 5 °C/min to 350 °C (PVDF), 420 °C (NH 4 HF 2 ), or 450 °C (PTFE) for 12 h and cooling at the same rate with intermittent grinding. These temperatures were selected to be high enough such that each fluoridating agent would undergo appreciably fast decomposition and low enough that hydrolysis of fluoride-containing products might be suppressed. − Additionally, an initial prereaction step for HfO 2 + NH 4 HF 2 samples with a ratio of 1:3.5, stoichiometric for production of (NH 4 ) 3 HfF 7 , was performed at 250 °C for 12 h to promote conversion into this desired precursor. All reactions with NH 4 HF 2 were carried out in air in capped Al 2 O 3 crucibles, while reactions with PTFE or PVDF were carried out in both capped Al 2 O 3 crucibles (20 mL) in air and in evacuated and sealed fused silica tubes.…”

“…The traditional solid-state approach is to combine precursor oxides and fluorides together and heat them until a reaction occurs. The high reactivity of all but the most stable fluoride materials with SiO 2 and/or water means that this often entails costly setups such as sealed metal tubes. − Alternative methods include exposing the precursor oxide to a reactive fluoride source such as F 2 or HF gas or aqueous hydrofluoric acid, although these must be handled carefully as they are highly toxic. , Safer options include controlled decomposition of stable fluorides and fluoride hydrates or reaction of oxides with solid fluoridation agents such as XeF 2 , CuF 2 , ZnF 2 , NH 4 F (or NH 4 HF 2 ), polytetrafluoroethylene [PTFE; −(CF 2 ) n −], or polyvinylidene difluoride [PVDF; −(CH 2 –CF 2 ) n −], all of which decompose upon heating into more reactive agents. ,,− Of these, the last three are stable under ambient conditions, therefore easy to work with, and conveniently produce volatile products at high temperatures, lowering the risk of secondary phase contamination. As such, these three reagents are commonly used to fluoridate oxides. ,,,, Among the hafnium oxyfluoride studies in the literature, it appears that primarily thermal decomposition of fluorides and reaction of HfO 2 with F 2 or HF have been attempted, whereas a wider variety of synthetic approaches have been used for Zr. − ,− Thus, employing a different fluoridation method for HfO 2 may reveal previously unreported Hf–O–F phases.…”

Network Structure Modification‐Enabled Hybrid Polymer Dielectric Film with Zirconia for the Stretchable Transistor Applications

“…Interestingly, these absorption peaks bleached the cross‐linker and zirconia‐loaded PcP films, suggesting that the chemical reaction between the hydroxyl group and cross‐linker can reduce the concentration of hydroxyl groups in the film. In addition, the absorbance peak near 870 cm ‐1 for all hybrid films was attributed to the existence of a Zr–O bond, which can be explained by the creation of ZrO 2 via the hydrolysis reaction of ZrCl 4 . The discernible peak at 980 cm ‐1 for the PcP‐DDTMS‐Zr0.2M film was identified from the vibration mode of Si–O–Zr, indicating that the DDTMS provides a silanol to the zirconium‐containing molecule .…”

“…In addition, the absorbance peak near 870 cm −1 for all hybrid films was attributed to the existence of a Zr-O bond, which can be explained by the creation of ZrO 2 via the hydrolysis reaction of ZrCl 4 . [35,36] The discernible peak at 980 cm −1 for the PcP-DDTMS-Zr0.2M film was identified from the vibration mode of Si-O-Zr, indicating that the DDTMS provides a silanol to the zirconium-containing molecule. [37,38] The PcP-BTMSH-Zr0.2M film exhibited an additional absorption peak at 930 cm −1 , which comes from the vibration of Ph-O-Si.…”