Relation between CLR Grammar and Ambiguity
A grammar may be may unambiguous, but not parsable by a LR(k) parser.
It is actually possible that a language has an unambiguous grammar,
but cannot be parsed deterministically by any PDA, hence has no LR(k)
parser.

For example the language $\{a^nb^n\mid n&gt;0\}\cup\{a^nb^{2n}\mid n&gt;0\}$.
It is clearly unambiguous (it is easy to write an unambiguous grammar for it). But, informally, there is just no way you
can decide which way you want to parse before you have read all the
$a$ and as many $b$.

An ambiguous grammar may define a language that has another grammar
that is not ambiguous, and may even be CLR(1) or LR(0). Actually, you
can just take an LR(0) grammar and add a few useless rule to make it
ambiguous without changing the language.

However, there are context-free languages that are inherently
ambiguous, i.e. that can only be defined by an ambiguous grammar.
And of course, there is no way an inherently ambiguous language can be
parsed deterministically.