The phrase "a relatively large amount of" is correct and usable in written English.
It can be used when discussing quantities that are significant in comparison to other amounts, but not excessively large.
Example: "The study revealed that there is a relatively large amount of data supporting the hypothesis."
Alternatives: "a considerable amount of" or "a significant quantity of".
XPS analysis of the plasma-treated materials reveals that a relatively large amount of copper, about 11% relative to carbon, is implanted into the near surface region.
Why? Traditional rechargeable cells leak a relatively large amount of power, whether being used or not.
New York City still has a relatively large amount of outstanding debt, forcing it to spend a big chunk of its annual tax revenue on those bills.
But periodically, a relatively large amount of energy is transferred to an electron by a nearly head-on collision along the path of the primary ionizing particle.
To compensate, the kidney (which has large glomeruli) produces a relatively large amount of dilute urine (about 20 percent of the body weight per day).
There is a relatively large amount of disagreement in the Florida polls — more than in the first three early-voting states.
First among these features is its high specific heat i.e., a relatively large amount of heat is required to raise the temperature of water.
Much of Staten Island's growth was centered in the southwestern part of the island, in places like Tottenville, where there was a relatively large amount of new construction in the 1990's.
On the other hand, it does require a relatively large amount of memory.
Plant fibre composites contain typically a relatively large amount of porosity which influences their performance.
By weighting the utility function from (9) by, operators act more actively to get their payoff when there is a relatively large amount of unused spectrum and more passively when there is a relatively large amount of spectrum loss.
