Synthesis of metastable t-ZrO2 via solid-state thermolysis of ZrOCl2·8H2O/NaHCO3: thermodynamics, oxygen vacancies, grain growth and phase stability
Abstract
We present a comprehensive multiscale theoretical framework for the topotactic solid-state thermolysis of ZrOCl2·8H2O and NaHCO3 (1:2 molar ratio) to metastable tetragonal zirconia (t-ZrO2). Six quantitatively coupled sub-models are developed and validated against experimental data [1]: (i) a thermodynamic Hess-cycle analysis yielding ΔG°topo = −287 ± 18 kJ mol-1 per Zr at 400 °C, which is 56 ± 28 kJ mol-1 more negative than the sol–gel benchmark; (ii) a surface-energy crystallite stability model predicting a critical size Dcr = 13.5 ± 2.0 nm at 400 °C, consistent with the experimentally observed coherent scattering region (CSR) of 11.3 nm; (iii) an oxygen-vacancy thermodynamic model with ΔGvacancy = −3.7 to −36.8 kJ mol-1 for O/Zr = 1.63–1.98, rationalising the uniquely reductive micro-atmosphere of the solid-state route; (iv) a gas-wedge fragmentation model with ℱ = 2.07–4.17, confirming primary particle breakdown to 40–80 nm prior to t-ZrO2 crystallisation; (v) a JMAK kinetic analysis of the t → m transformation giving Ea = 81 ± 6 kJ mol-1 and Avrami exponent n = 0.27–0.31, consistent with defect-driven surface nucleation; and (vi) a grain-growth model with Q = 185 ± 15 kJ mol-1 in the presence of NaCl, representing a 25–40 kJ mol-1 reduction compared to NaCl-free systems. A (D, x)-phase stability map predicts a re-entrant t → amorphous boundary at O/Zr < 1.60 for D < 5 nm — a novel, falsifiable prediction — and quantitatively reproduces all experimental phase fields from ref. [1]. The by-product NaCl acts as a dual-role flux, stabilising t-ZrO2 nanoparticles below 500 °C via grain-boundary pinning but accelerating grain coarsening and the t → m transition above 600 °C. Optimal synthesis conditions are established: 1:2 molar ratio, heating rate β = 8–12 °C min-1, calcination at 350–450 °C, and post-synthesis drying at 55–65% relative humidity.
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BibTeX
@misc{трихліб2026synthesis,
title = {{Synthesis of metastable t-ZrO2 via solid-state thermolysis of ZrOCl2·8H2O/NaHCO3: thermodynamics, oxygen vacancies, grain growth and phase stability}},
author = {Володимир Трихліб},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009693/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009693/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Synthesis of metastable t-ZrO2 via solid-state thermolysis of ZrOCl2·8H2O/NaHCO3: thermodynamics, oxygen vacancies, grain growth and phase stability
AU - Володимир Трихліб
PY - 2026
DA - 2026/09/30
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009693/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009693/v1
AB - We present a comprehensive multiscale theoretical framework for the topotactic solid-state thermolysis of ZrOCl2·8H2O and NaHCO3 (1:2 molar ratio) to metastable tetragonal zirconia (t-ZrO2). Six quantitatively coupled sub-models are developed and validated against experimental data [1]: (i) a thermodynamic Hess-cycle analysis yielding ΔG°topo = −287 ± 18 kJ mol-1 per Zr at 400 °C, which is 56 ± 28 kJ mol-1 more negative than the sol–gel benchmark; (ii) a surface-energy crystallite stability model predicting a critical size Dcr = 13.5 ± 2.0 nm at 400 °C, consistent with the experimentally observed coherent scattering region (CSR) of 11.3 nm; (iii) an oxygen-vacancy thermodynamic model with ΔGvacancy = −3.7 to −36.8 kJ mol-1 for O/Zr = 1.63–1.98, rationalising the uniquely reductive micro-atmosphere of the solid-state route; (iv) a gas-wedge fragmentation model with ℱ = 2.07–4.17, confirming primary particle breakdown to 40–80 nm prior to t-ZrO2 crystallisation; (v) a JMAK kinetic analysis of the t → m transformation giving Ea = 81 ± 6 kJ mol-1 and Avrami exponent n = 0.27–0.31, consistent with defect-driven surface nucleation; and (vi) a grain-growth model with Q = 185 ± 15 kJ mol-1 in the presence of NaCl, representing a 25–40 kJ mol-1 reduction compared to NaCl-free systems. A (D, x)-phase stability map predicts a re-entrant t → amorphous boundary at O/Zr < 1.60 for D < 5 nm — a novel, falsifiable prediction — and quantitatively reproduces all experimental phase fields from ref. [1]. The by-product NaCl acts as a dual-role flux, stabilising t-ZrO2 nanoparticles below 500 °C via grain-boundary pinning but accelerating grain coarsening and the t → m transition above 600 °C. Optimal synthesis conditions are established: 1:2 molar ratio, heating rate β = 8–12 °C min-1, calcination at 350–450 °C, and post-synthesis drying at 55–65% relative humidity.
ER -