You will be shown an abstract from a materials science research paper. Your task is to extract all synthesis operations described in the abstract into a structured JSON format. Your output should be a JSON array. Each entry in the array should be a JSON object describing a single synthesis operation. This object should have the following fields:

- "trigger": A verbal predicate indicating a synthesis operation. This should be a string extracted directly from the abstract.
- "arguments": An array of arguments specifying aspects of the synthesis operation. Each entry in the array should be a length-2 array formatted as [<argument_text>, <argument_type>]. The `argument_text` should be a string extracted directly from the abstract. The `argument_type` should be one of the following types: ["Recipe_Precursor", "Atmospheric_Material", "Participant_Material", "Recipe_Target", "Solvent_Material"].

For instance, suppose an excerpt from the abstract reads:

Tetraethoxysilane (TEOS, 98%) and cetyltrimethylammonium bromide (CTAB, 98%) were purchased from Fluka. The MTTZ-siloxy derivative (triethoxysilyl-propyl-5-mercapto-1-methyl-tetrazole) was synthesized as previously described [38].

This excerpt includes two operations, which could be annotated as follows.

[{"arguments": [["Tetraethoxysilane", "Recipe_Precursor"], ["cetyltrimethylammonium bromide", "Recipe_Precursor"]], "trigger": "purchased"}, {"arguments": [["MTTZ-siloxy derivative", "Recipe_Target"]], "trigger": "synthesized"}]

In your response, please include the JSON and no other text.

Abstract:
10.1016/j.solidstatesciences.2016.09.005
Dielectric properties of FeNbO4 ceramics prepared by the sol-gel method

FeNbO4 powders were prepared using the sol-gel method. Niobium chloride (NbCl5) and iron nitrate (Fe(NO3)3*9H2O), were used as starting materials and citric acid and ethylene glycol as chelating agent and reaction medium, respectively. All reagents used in the process were of analytical grade. A suspension containing stoichiometric amounts of starting materials was previously prepared in a minor amount of hydrogen peroxide (3% V/V) and dispersed in a mixture of citric acid and ethylene glycol in a molar ratio 1:3. In order to promote the solubility, the suspension was stirred until a clear colloidal suspension was obtained.

The solution was dried at 300 degC for 24 h to evaporate the solvent and the obtained powders were thermally analysed by differential thermal analysis, performed in a Lynseis Apparatus type L92/095, in the temperature range 20-1200 degC, with a heating rate of 5 degC/min, using Al2O3 as reference.

Subsequently, the dry powders were pressed into pellets, and finally heat-treated, according to the DTA results, at 500, 650, 850, 1000 and 1200 degC, using a dwell time of 4 h, with a heating rate of 5 oC/min.
[{"arguments": [["FeNbO4", "Recipe_Target"]], "trigger": "prepared"}, {"arguments": [["iron nitrate", "Recipe_Precursor"], ["ethylene glycol", "Participant_Material"], ["Niobium chloride", "Recipe_Precursor"], ["citric acid", "Participant_Material"]], "trigger": "used"}, {"arguments": [["suspension", "Participant_Material"], ["hydrogen peroxide", "Participant_Material"]], "trigger": "prepared"}, {"arguments": [["ethylene glycol", "Participant_Material"], ["citric acid", "Participant_Material"]], "trigger": "dispersed"}, {"arguments": [["suspension", "Participant_Material"]], "trigger": "stirred"}, {"arguments": [["solution", "Participant_Material"]], "trigger": "dried"}, {"arguments": [["powders", "Participant_Material"]], "trigger": "thermally analysed"}, {"arguments": [["powders", "Participant_Material"]], "trigger": "pressed"}]