How Can a Researcher Correctly Prepare Ba3(PO4)2 Instead of Ba(HPO4)?

[Soaring Crane]

Suppose there is a researcher at a chemical company whose job is to create the compound barium phosphate. BaCl2*2H2O and (NH4)2HPO4 was mixed together in a water solution. However the compound that formed was not the desired Ba3(PO4)2 but Ba(HPO4).
How can the researcher prepare the correct solution?
Wanted reaction: 3BaCl2 + 2(NH4)2HPO4 --> Ba3(PO4)2 + 4NH4Cl + 2HCl
Reaction in reality: BaCl2 + (NH4)2HPO4 --> Ba(HPO4) + 2NH4Cl
Well, there would need to be a 3:2 ration of barium chloride and phosphate compound instead of 1:1.
If there is a set M of 0.6 M for each reactant, the vol (L) can be changed so 5 L of BaCl2 yields 3 mol and 3.33 L of (NH4)2HPO4 yields 2 mol?? Are there other ways (changing M) to achieve the desired results?
Thanks.

 

[GCT]

try thinking about the reverse reaction, the differences in the condition of dissolution of Ba3(PO4)2 and that of Ba(HPO4) is simply that the first is done in an more acidic solution (that probably means that it's less soluble than the amphoteric salt). PO4 3- is being consumed by the acidic solution, to HPO42-. Assuming that Ba(HPO4) is also slightly insoluble, then it will now precipitate.