Hello , I am from china ,I can tell you That we usually don't directly use one word 聊， usually 聊聊 Is equal to聊天 ，If it's useful then I will be very happy

聊天 is separable verb(verb+noun), 聊+duration+天、聊+着+天、聊+过+天.....,so we can say: 聊了两个小时天（chat for two hours),聊着天（chatting）,聊过天（chatted ). 聊 is a verb，聊+object，so we can say 聊旅游（talk about travel)、聊生活（talk about life)、聊了两个小时......

“昨天我们聊了很久。”"We had a long chat yesterday."In this sentence, “聊” is a verb. “不要打扰他们聊天。”"Don't interrupt their conversation." In this sentence, “聊天” is a noun.

To make it simple, we can say 聊聊： 我们聊聊啊？， 我们聊什么呢？，我们聊十分钟吧。 聊天 is a noun or a intransitive verb. We say: 聊天使人轻松。我喜欢和人聊天。

hi, I look up in some books and find the following explanation for you . Hope it is helpful. Because these two words are different in it's construction, there are some differences in the usage. 1.聊天 is a verb-subject word, so when it is used as verb predicate, it Cann't be followed any objects while 聊 has not this restriction; eg. 我们聊天童年的往事。 X 我们聊了很多童年的往事。 2. 聊天 is a 离合词 （separable words), so when it is followed with tense particle or complements, the verb is usually separated from the object, while 聊 can be directly followed by the tense particle or complements. eg. 我们聊了好久的天。 他们正在那聊着天。 我们正聊着。 我们聊了好久。 3. when a complement of state expressing how the actions is going on is used after, usually 聊 is used. not 聊天。 大家聊得开心极了。 if you want to use 聊天， you should repeat the v. by saying 大家聊天聊得开心极了。