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:
10.1039/c6dt02166b
Magnetic and thermoelectric properties of the ternary pseudo-hollandite BaxCr5Se8 (0.5 < x < 0.55) solid solution

In order to prevent oxidation of the reactants and of the products, all manipulations were performed under an inert gas atmosphere or under vacuum (glove box or sealed containers). The elements, Ba (rod, 99+%), Se (shots, 99.999%) and Cr (powder -325 Mesh, 99%) all from Alfa Aesar, were used as received. The synthesis of the solid-solution samples was performed following ref. 20. BaSe was prepared by mechanical alloying using appropriate amounts of the elements (10 g total) loaded in 20 ml tungsten carbide jars and using 7 balls of the same material. The mechanical alloying synthesis was achieved using a Fritsch Pulverisette 7 PL, with a program of 15 cycles of 2 minutes at a speed of 700 rpm. BaxCr5Se8 was then prepared from an appropriate amount of BaSe and elemental Cr and Se. In order to obtain 5 g of the title phase, precursors were ground, mixed and placed in an alumina boat in a sealed silica tube, and heated to 873 K in 10 hours, the temperature at which it remained for two days. The mixture was then slowly cooled to room temperature within 10 hours and a homogeneous dark grey powder was obtained. The powder was compacted using spark plasma sintering (FCT HP D 25/1) in order to produce dense samples for physical property measurements. About 5 g of the sample were inserted into high density graphite dies (Carbonloraine) with an inner diameter of 15 mm. The temperature was raised in 45 minutes to 973 K, this temperature plateau lasted 40 minutes before a 45 minutes ramp down to room temperature. The pressure was raised from 28 MPa to 50 MPa during the heating step, kept constant over the temperature plateau and released during the cooling step. Bulk densities of each sample were determined by the Archimedes method using ethanol as the flooding liquid and were found to be over 95% of the theoretical densities. The samples were stored in air and were checked multiple times using XRD measurements, which showed no sign of degradation or oxidation after several weeks.
[{"arguments": [["inert gas", "Participant_Material"]], "trigger": "performed"}, {"arguments": [["Se", "Recipe_Precursor"], ["Ba", "Recipe_Precursor"], ["Cr", "Recipe_Precursor"]], "trigger": "used"}, {"arguments": [["samples", "Participant_Material"]], "trigger": "performed"}, {"arguments": [["BaSe", "Participant_Material"]], "trigger": "prepared"}, {"arguments": [["elements", "Participant_Material"]], "trigger": "using"}, {"arguments": [["material", "Participant_Material"]], "trigger": "loaded"}, {"arguments": [["BaSe", "Participant_Material"], ["Cr", "Recipe_Precursor"], ["BaxCr5Se8", "Recipe_Target"], ["Se", "Recipe_Precursor"]], "trigger": "prepared"}, {"arguments": [["precursors", "Participant_Material"]], "trigger": "ground"}, {"arguments": [["mixture", "Participant_Material"]], "trigger": "cooled"}, {"arguments": [["powder", "Participant_Material"]], "trigger": "compacted"}, {"arguments": [["samples", "Participant_Material"]], "trigger": "produce"}, {"arguments": [["sample", "Participant_Material"]], "trigger": "inserted"}]